How to adjust a dual flush toilet mechanism

You may or may not know what dual flush is, but is there really any benefit to it? Lets take a look.

How to adjust a dual flush toilet mechanism

How to adjust a dual flush toilet mechanism

Dual Flush is an interactive water saving design for a toilet. It is created with the internal flush valve allowing two separate flushing volumes for disposing waste. This type of cistern gives you the choice between a half flush for disposing liquid waste or a full flush for disposing solid waste.

This image shows how much water is left in the tank for a half flush (left) and full flush (right)

There are currently two different types of dual flush valves which you can install. Firstly there is a toilet syphon which is operated by a toilet handle (For more information on how a dual flush syphon works, check out our article How a Dual Flush Syphon Works.), or a dual flush drop valve which can be operated by either a lever handle or a push button.

Think you don’t waste much water?
Thanks to a factsheet from Waterwise we have the following water usage data:

How to adjust a dual flush toilet mechanism

As you can see flushing your toilet uses more water than any other household item totaling to 30% of all consumed water.

How much water would I save with a half flush?

How to adjust a dual flush toilet mechanism

Most toilets have a flush volume of 6 litres and half flush of only 3. This means that each half flush would save 3 litres of water. To put this into perspective, each half flush will save more than your recommended daily intake of water! This could equate to a massive saving of 24 litres (over 40 pints) of water per person each day, and of course, a massive saving on your water bills.

To sum it up
A dual flush toilet is something that should not be overlooked as they are easy to install and will fit into your current toilet cistern. Whether it be a replacement toilet syphon or a drop valve, they will be readily available in your nearest plumbers merchants and at a relatively low cost.

For more information please check out our other articles, and if you found this article to be helpful then don’t forget to share!

How to adjust a dual flush toilet mechanism

The ball in the toilet is a water fill regulating device. Also known as the toilet float, it is as simple as it is effective, and has been a staple in toilets for decades. They are attached to a long metal rod that connects to the toilet fill valve. Newer model toilet valves have done away with the traditional toilet ball, but there are many toilets still made and still in use that use a toilet ball to regulate how high the water level fills into a toilet tank.

Remove the toilet tank cover and set it off to the side. Be careful. Most tank covers are made of ceramic and will crack if dropped.

Locate the toilet ball inside of the toilet. If the tank is full, it will be floating on top of the water opposite the side of the handle. If the tank is full and the ball has sunk, it is no longer useful and needs to be replaced. The floating ball regulates the water level inside of the tank. The higher the ball sits inside of the tank, the higher the water level will be. If the toilet is constantly running, the toilet ball is sitting too high in the toilet and needs to be lowered. If the ball sits too low in the tank and the flush is not adequate, the ball must be raised.

Adjust the toilet ball by turning a screw on the toilet valve. The ball rod connects into the toilet valve and this is where you will find an adjusting screw.

Turn the screw clockwise to lower the ball, and thus, lower the water level. By turning the screw counterclockwise, you will raise the ball and raise the corresponding water level.

If you do not have a screwdriver,, grasp the toilet ball rod in your hands and slightly bend it upwards to fill the tank more. This will cure an inadequately flushing toilet. To cure a constantly running toilet, grasp the toilet bowl rod and bend it down slightly. This will lower the water level in the tank and stop the toilet from running.

Dale Yalanovsky has been writing professionally since 1978. He has been published in "Woman's Day," "New Home Journal" and on many do-it-yourself websites. He specializes in do-it-yourself projects, household and auto maintenance and property management. Yalanovsky also writes a bimonthly column that provides home improvement advice.

The dual flush toilet is one of the important inventions of technology. It is helping us to save a billion gallons of water every day by decreasing the needs of water in our toilet. Moreover, you can adjust the water level up to certain level easily. Less water also means less water bill.If you are searching for a guide on how to adjust dual flush toilet mechanism, then keep reading this article.

Here we will let you learn how to do it as well as teach you how to solve the common problem of dual flush toilet mechanism.

The history of dual flush toilet mechanism

A dual flush toilet is a version of the usual flush toilet that comes with two buttons or includes a handle mechanism to flush different quantity of water. The mechanism was first developed by a Japanese product manufacturer known as TOTO during the 90s. The product included two levers along with a hand washer. The revolutionary product was, fortunately, capable of reusing the water that you used for hand washing for flushing.

The product was not that popular outside Japan. In 1976, American industrial designer Papanek Victor proposed a real-world friendly design of the dual flush system in one of his book. Then at 1980, the design was first implemented by an Australian sanitary-ware company. It has flush volumes of 5.5 liters and 11litres. After that, the product becomes very popular in Australia, New Zealand, Singapore, and other countries.

Dual flush mechanism – how it works

As the dual flush mechanism toilet was developed in Australia and the developer designed with a view to the old traditional Australian flushing toilet, the push button varies from the old siphon flush toilet which relies on the gravity to remove things from the toilet. As it lacks the siphoning feature, this mechanism requires less water for operating.

In the dual flush mechanism toilet, the waterline is comparatively lower than the siphon flush toilets. The most impressive feature of the product is it includes two buttons in the cistern which allow you to release different quantity of water. The smaller button delivers three liters of water when the bigger button delivers six liters of water. The smaller button is designed to flush off the liquid waste, and the more prominent button is for the solid wastes. It also releases water faster with 10 cm trapway in the bowl, which helps to clean off the waste with less water.

The main benefit of the mechanism is it requires less water. Every day, we pollute thousands of tons of water every second, which is decreasing the supply of clean water. In such situations, the dual flush mechanism decreased water uses on a large scale with its proper design.

How to Adjust a Dual-Flush Toilet

Adjusting the dual flush motor requires adjusting the water level and the flush button. One thing we want to let you know that adjusting the dual flush motor doesn’t require removing the water from the water tank. You will require flushing the toilet while making the adjustments. Here are the step by step guides on how to adjust the dual flush toilet mechanism.

How to adjust a dual flush toilet mechanism

Step-1: Remove the tank lid off from the dual-flush toilet tank and put it in an upside down position. Make sure that you put it on a flat surface carefully. After removing the lid, you will find two rods which reconnected with the push buttons. Deal with them carefully as you end up by damaging them.

Step-2: There will be float adjustment screw in between the flush valve and fill valve. Now take a flat-head screwdriver and raise turn the adjustment screw at a clockwise direction. It should raise the water level to the indicator line on the backside of the toilet tank. Now turn the screw on a counterclockwise to decrease the water level.

Step-3: Now take the lid and carefully place it over the tank. As you have done it, you should test the flush buttons to know whether they can work or not. The smaller button should produce less water, and the bigger button should provide much water. Check the button, whether they work properly or not.

Step-4: If any adjustment required, then you should remove the lid again from the tank and put it in upside down position. Slacken the plastic nut with the help of nut. You will find them in the rod of the push button. Make sure that you are not removing the nut. Here, your purpose is to just lose the nut so that it can turn the push button.

Step-5: To lower the rod, run the push-button rod in a clockwise direction and counterclockwise to if you require extending. Now carefully tighten the plastic nut and put the lid back on its position. Now re-test the flush to check whether it works efficiently or not. If you require further adjustment, you can continue the adjustments.

The solution of the common problems in dual flush toilets

If the half/full flush closes instantly after you release the tank lever: If this happens, you should set the water level at a higher position. You shouldn’t use the duo flush if it doesn’t allow you to increase the water level. After setting the water level, set the adjustments dials at maximum. Now check whether it works or not.

If the fill valve turns off and on automatically – the problem is known as ghost flushing.It usually happens when the water tank is leaking in the bowl from one or multiple leaking point. Find the valve set and remove the dual flush valve. Then find the seat adapter and turn it in upside down and spread and reshape the putty ring. Make sure that the refill tube is clipped properly so that it doesn’t shove into overflow pipe directly.

Adjusting the dual flush toilet is not that easy. However, we hope that after reading the above guide, it will be easier for you.

A dual flush toilet flushing mechanism works different from that of a single flush toilet. Dual flush toilets mostly use flush buttons instead of a trip level and do not use the ordinary toilet flapper with a lift a chain.

The level of water inside a dual flush toilet tank will also affect the water level inside the bowl. If the toilet tank water level is too low it also means the water level in the bowl will also be low and vice versa.

A low water level in a dual flush toilet tank/bowl is a sign that the fill valve is faulty, toilet float is not properly adjusted, refill tube is not clipped on the overflow tube, toilet bowl is cracked or the vent stack is clogged.

Adjusting the water level in a dual flush toilet is however a simple task that only needs a screwdriver to fix. You might however need to replace the fill valve if it faulty.

How to adjust a dual flush toilet mechanism

It is first important to make sure that the low water level in your toilet is not as a result of leak. A running toilet will will continuously drain the water in the tank inside the bowl and will most likely ghost-flush.

Put some food color inside the tank and if the same appears inside the bowl you have a running toilet. I have written a whole post on how to fix a running dual flush toilet. Read it here.

A low water lever in a dual flush toilet tank is characterized by a low water level in the bowl and a weak flushing toilet. A high water level is characterized by a running or overflowing toilet.

Before you know how to adjust a dual flush toilet float, it is even better if you first understood how a dual flush toilet works. This will make fixing it easy and quick.

How Dual Flush Toilets Work

How to adjust a dual flush toilet mechanism

Push Button Valve Assembly

In a single flush toilet, the toilet handle is connected to a lift chain which in return is connected to the toilet flapper. During flushing, the chain lifts the flapper off and the water moves through the flush valve to the bowl.

A dual flush toilet has no lift chain. A solid push button assembly is installed in the middle of the tank. It has two buttons most in white and blue. One button is for the full flush while the other one is for the half flush.

When you push down one of the button, the flush valve seal is lifted off and water then moves down to flush the toilet.

Toilet Fill Valve

How to adjust a dual flush toilet mechanism

The toilet fill valve of a dual flush toilet does not differ from those of a single flush toilet. It is responsible for filling the toilet tank with water after every flush. A toilet fill valve is connected from the bottom of the tank to the water supply line.

Toilet Float

The float cup which is also known as a float cylinder is a cylindrical cup connected to the vertical body of the fill valve assembly. It regulates the opening and closing of the fill valve.

The float cup also regulates the level of the water in the toilet tank. If it is set too low, the level of the water in the tank will be low and hence low flushing power. If it is set to high, the water level in the toilet tank will be too high. If it goes higher than the overflow tube it will start running back to the bowl causing your toilet to run throughout.

Refill tube

The refill tube is a small tube connected from the fill valve to the overflow tube. After flushing and as the fill valve is refilling the tank, the refill tube send a little amount of water back to the bowl through the overflow tube.

The water remains at the bottom of the bowl. This water prevents sewer gases from coming up into the bathroom and entire house.

If the toilet is not filling up properly, sufficient water will not be sent back to the bowl and hence a low water level in the toilet bowl.

Overflow tube

The overflow tube a cylindrical tube in the middle of the toilet tank. If the toilet bowl is continuously filling with water, it prevents the flooding of the bathroom and entire house by sending the excess water back into the bowl. If therefore your toilet can’t stop running, this is normally the problem.

How to Adjust the Water Level in a Dual Flush Toilet

There are several ways to adjust the water level in a dual flush toilet depending on what is causing the problem.

1. Adjust the Toilet Float

  • Start by removing the toilet tank lid. Note that this piece is made of porcelain and could easily crack. Place it on safe place.
  • Note the level of water inside the tank. Ideally the water level inside the tank should be about a half inch below the top of the overflow tube. If it is lower than that or higher you need to adjust it.
  • Look for a long plastic adjustment screw attached to the toilet float and toilet fill valve as well. To adjust the level of water in the tank you will need to turn this screw.
  • Using a screwdriver, turn the adjustment counterclockwise to increase the water level in the tank and clockwise to lower the water level. Turn the screw slowly, as you do not want the water level to increase suddenly. You want to make sure that it is ¼ to ½ inch below the overflow tube.
  • Make sure that the refill tube is also properly clipped on the overflow tube and in good condition. One of the reasons that some toilet bowls have a low water level is because the refill tube is not properly clipped. Make sure that it is not also too long inside the overflow tube that it is siphoning water out of the bowl.

2. Replace the Fill Valve

Sometimes the low water level in a dual flush toilet is caused by a faulty fill valve. This is especially the case in areas with hardwater, where the fill valve is blocked by mineral deposits and other debris.

It could also be that the toilet fill valve’s seal is worn out causing the toilet to run throughout. Fixing a toilet fill valve is possible but the best thing to do is to replace it with a new one.

Toilet fill valves are really cheap and easy to install. I have written a detailed post on how to replace a toilet fill valve. Read it here.

3. Unclog the Toilet Drain/Vent Stack

A partially clogged toilet or a blocked vent stack will slowly siphon out water out of your toilet bowl. This happens regardless of whether it is a single flush or dual flush toilet.

Unclogging the toilet and/or vent stack will easily fix this problem. I have also written a log post on how to ho about this problem. Find it here.

As we advance our footsteps in new technologies it often turns out to be a bit intricating as we always look for a guide to answer our question like how to adjust water level in dual flush toilet? To understand these first let us go through the dual flush concept.

Dual Flush Concept

A dual flush toilet is an advanced variation of the standard flush toilet mechanism first developed by a Japanese sanitary product manufacturer in 1960. It was designed as a revolutionary product, equipped with dual levers and built-in hand washer that rehash the water in the hand washer for flushing.

The dual flush toilet mechanism became almost popular and is widely adopted in Europe, Australia, and Asia and they are being used in other areas as well. The increased environmental awareness, the government regulations, the rising cost of water and the availability of monetary incentives are making people around the world to switch over to dual flush and low flow toilet designs as the most attractive method in the present sanitation market.

Dual Flush Mechanism

How to adjust a dual flush toilet mechanism

The mechanism of the dual flush toilet is designed with a push- button dual flush feature that release different volumes of water depending on whether it is a liquid waste or a solid waste. In addition, it also differs from conventional siphon flush toilets as the removal of these features also means that the toilet requires less water to operate.

The standard toilets use siphoning action, a method that employs a high volume of water entering the toilet bowl because of the air that enters the tube as the flush is pressed which makes the system ineffective and drain a large amount of water to clean the solid or liquid waste.

The construction of the dual flush technology is developed with two operating buttons on the cistern which release different volumes of water: one button delivers six litres and the other three. The larger quantity is designed to flush liquid waste.

For effective cleaning, the bowl of the dual flush toilet is designed with a larger 10 cm trap way (the hole at the bottom of the bowl) allowing for water to come out faster and clear the bowl effectively. As there is no siphoning action involved, on per flush the system needs less water and the large diameter trap way makes it easy for waste to exit the bowl.

Moreover, the half-flushes for liquid waste combined with the effective large flush treatment can save up to 68% more water than a conventional low flow toilet. The mechanism of the dual flush toilet uses a larger diameter trap way that works more effectively and clog less than the conventional siphon toilet. It needs less water to flush efficiently and save more water than a low flow toilet when flushing liquid waste.

How to adjust a dual flush toilet mechanism

Water is leaking from the tank into the bowl at one or more leak points. Follow the steps below:

  1. Remove the Duo Flush valve from the valve seat and clean both the Duo Flush seal and the plastic seat the seal sits upon.
  2. Pull angled seat adapter straight up until it pulls free from flush valve seat. Turn adapter upside down and reshape putty ring, spread putty evenly around entire base of adaptor.
  3. Check the black seal at the base of your original flush valve/ overflow pipe unit. If you get black residue on your fingers when you touch the seal, replace the flush valve. If seal is good reseat angled seat adaptor.
  4. Inspect the overflow pipe for obvious cracks.
  5. Make sure the refill tube (rubber hose) is clipped to the side of the overflow pipe and not directly shoved into the overflow pipe.
  6. Replace Duo Flush onto valve seat and turn on water, check for leaks.

4. Removing the Duo Flush valve from the seat

  1. Gently rock the Duo Flush canister away from the overflow pipe and pull up.

5. Removing the activation box (both newer and older versions of the converter) once it has been snapped onto to the tank lever.

  1. On older versions of Duo Flush, grab hold of the activation box in the tank and pull it toward the back of the tank. You may need to give it a strong jerk to unsnap it.
  2. On newer versions on the Duo Flush, there is a push button on top of the activation box. Simply push in the button and pull away from the tank lever.

6. The tank lever sticks in the up or down position, it does not return to a horizontal position after you flush.

Remove the toilet lever from the tank and remove the black spacer from the tank lever spacing nut, follow these steps:

  1. Push the button on the top of the actuator handle box and release the box and cable from the tank lever thread.
  2. Remove the lock nut from toilet handle thread; this is a reverse threaded nut, turn nut counterclockwise to release the nut.
  3. Remove the toilet handle from the front of the tank.
  4. Remove the black rubber (square shaped) spacer from tank lever’s spacing nut.

Replacing tank lever:

  1. Replace tank lever back into the tank’s lever mounting hole. Make sure to push the lever all the way in ensuring the tank lever is flush with the face of the tank.
  2. Tighten lock nut onto the tank lever thread; this is a reverse threaded nut, turn nut clock wise to tighten nut.
  3. Snap actuator box onto tank lever thread.
  4. Replace the tank lever without the spacer and retry the flush.

Or Download the Duo Flush System Toilet Converter installation instructions

How to adjust a dual flush toilet mechanism

Dual flush toilets are trendy these days, and you might have used one and haven’t noticed. I know I was like that at some point! But even though you have used them, the question is, do you even know how the dual flush toilets work? This piece will educate you on all the pros of getting the double flush toilet.

I know the two buttons can confuse anybody trying to flush the toilet. They look very much like the traditional water closets that we’re all familiar with on our day-to-day lives. Though the toilet is quite efficient in areas with less amount of water. So, using the toilet, saves you the stress of using excess water while carrying out a flush. I don’t think it would be a dragon-slaying task if you don’t have so much water to flush when it is necessary.

Dual Flush vs Single Flush Toilets

How to adjust a dual flush toilet mechanism

There is one single difference between the dual flush toilets and the traditional single toilets amongst the myriads of similarities.

This is simple! It is the way they both use the water to dispose of /flush waste. Dual flush toilets flush differently from the traditional variants. It all depends on if you are flushing liquids or not. Liquid wastes flush significantly quicker and more comfortable than hard or solid waste.

For someone who is cautious about his or her environment, this can be seen as God’s gift to them. They can be convenient in conserving water in places where water shortage is experience. At the close of the day, I think dads are going to love this too because, when used properly, it is often accompanied with lots of budget friendly benefits.

The dual flush toilets are common, and you might have seen one but have not been attentive to them. When viewed at first, they can be confusing. Once you know how it operates, everything becomes simple and clear. The toilet is accompanied with pros and cons.

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How Does a Dual Flush Toilet Work?

How to adjust a dual flush toilet mechanism

The traditional toilets use the tube as a way to remove waste from the toilets bowl. This technique, when compared to the dual flush toilet, is entirely different. In a simple traditional toilet, large volume of water is necessary to pull the waste down the toilet bowl.


The dual flush’s method is different from the conventional glow. The hole at the bottom of the toilet bowl is larger. So this enable it to pulls-down waste with minimal water level. This feature gives it a unique touch.


The biggest thing about the dual flush is the amount of water it saves. Letting whoever is using the toilet a two flush modes as the name suggests this means that they keep the water about three times more than the conventional flush systems. One can save 68 percent of water using a dual flush; this makes the toilet budget-friendly.


Just like it saves water, money is also saved with the dual flush. Of course, you are going to need that extra money for something else like books for the children or whatever treat necessary.

The mechanism

The dual flush toilets do not have any tube action, this makes the use of plunger less valuable. All it has is a large hole at the bottom for easy flush with less water and less power. So, forget about all of the stress that the traditional flushers bring and go get your dual flush toilet plunger.

In as much as the plunge is going to be idle for the main time, the toilet brush will be your most useful tool. Since the water doesn’t generate too much power, you are going to use the brush often. Installing the dual flush toilet doesn’t require too much effort. It is just like the traditional single flush.

Bestseller No. 1 How to adjust a dual flush toilet mechanism

How to adjust a dual flush toilet mechanism

While toilets are built to regulate the amount of water that they use, it is still sometimes necessary to adjust your toilet fill valve. Whether you are trying to conserve water by reducing the amount you use with each flush, or trying to fix a toilet that does not flush with enough strength to work properly, adjusting the fill valve is something that requires some careful effort. However, there is no reason that you cannot adjust your own without professional help, as it requires no special tools or skills. What follows should give you everything you need to know about how to make this adjustment.

Step 1 – Find the Fill Valve

Before you can do anything, you will need to locate the fill valve in your toilet tank. First, set up a towel flat on the floor. Then, remove the top of the tank to open it up, and lay it down on your towel. You should see a mechanism with a device that floats at the surface of the water somewhere inside. This device can vary between models and appear very different. For example, sometimes there will be a device that floats attached to a metal arm. In other models, the floating device is a cylinder that surrounds a pipe. Either way, the purpose is the same—to detect when enough water has entered your toilet tank and stop the flow. Thus, to change the amount of water used in a flush, your goal is to adjust the mechanism that the floating device is attached to.

Step 2 – Adjust the Height

To adjust your toilet’s fill valve, you will first have to decide which direction to adjust it in. No matter what sort of model your toilet is, adjusting the floating device to sit higher will allow your toilet to put more water in the tank before shutting off, so you should do this if you want to increase the water flow when you flush. If, on the other hand, you want to reduce water use, you should adjust the floating device to be lower, so that less water is allowed inside before this valve shuts off the flow.

The specifics are slightly more varied between the different types of toilet fill valves. If your toilet has an arm mechanism that rotates, you should be able to adjust a screw at the point of rotation to adjust the height of the floater. In extreme cases, if the fill valve is damaged or inaccessible, you might be able raise or lower the floater by simply bending the metal arm, in the case that you don’t wish to replace it. On the other hand, if your toilet has a cylindrical floater that surrounds a pipe, there should be a spring that you can press to release the floater so that you can adjust it up or down. Once you have adjusted it, tighten the screw or re-engage the spring device.

Step 3 – Finishing Up

Make sure everything is secure and as it should be before giving your toilet a test flush. It should work as planned, but you may need to adjust further to have the perfect amount of water in each flush.

I have summarized the discussion. You may have a look at the summary first. For more in detailed info, you may read the Explanation section at the bottom. Refer to the pictures and the text on the pictures for better understanding of what I had written.


Overall Water Output

If you do not understand what I had written, just follow these rules to adjust the overall water output from the water tank into the toilet bowl. When I talked about overall, it means whether you pressed the left or right button, it produces the same result.

1. Push the slider down, push the square button down, MAX water flowing out

2. Push the slider up, push the square button up, MIN water flowing out

Making the left button have lower water output than right button.

1. Adjust the length of the button(adjust the nut) on the left to make it shorter. If it can’t be adjusted, cut it but PLEASE BE VERY CAREFUL with the cutting and if you made a mistake cutting it, you may need super glue to put it back (BEWARE). The reason why a shorter rod produces less water output is because it can only push the button at the top of the canister partially and not completely(not long enough).

If you prefer the right button to have lower output than the left, reduce the length of the right rod.

If you can’t understand after reading it, feel free to contact me.

Explanation: Dual Flush Toilet Mechanism water output – How it works

How to adjust a dual flush toilet mechanism

On the top of the water tank, there are 2 buttons. The water output differences between these 2 buttons are determined by the length of the 2 rods at the bottom of these 2 buttons.

How to adjust a dual flush toilet mechanismTo make both of these 2 buttons with different water output, you need to shorten the length of one of these 2 rods. The adjustment can be done by adjusting length of the rod or if it can’t be adjusted, you need to cut/shorten the rod. The shorter rod would have lower water output because it can only pressed down the top button of the canister partially and by how much is dependent on its length.

How to adjust a dual flush toilet mechanism How to adjust a dual flush toilet mechanismHow to adjust a dual flush toilet mechanismHow to adjust a dual flush toilet mechanism

If you look at the the water output controller tower/canister, you will see that there are 2 mechanism, namely the Slider and the Square Button which can be adjusted.

a) Square Button

At the SIDE, near the BOTTOM, you will see a small square button where it can pulled up or down. For this small square, its function is just to control the water flowing out from the canister. If the button is push to the bottom, it closed the square hole entirely, meaning water coming out from the square button would be much slower. When water flow out slower from the square hole, the shutter which prevent water flowing out into the toilet bowl will move down slower and causes water to flow into the toilet bowl for a much longer time because it takes the shutter longer time to close the hole which lead water into the toilet bowl.

b) Slider

At the SIDE of the output canister, you will see a structure which looked like a ruler. Attached to the ruler is a slider which can be pull up or down. This structure has the same function as the square hole which we discussed earlier on except that it control the water output in another way. When we pull up the slider which is attached to the ruler , less water going to flow into the toilet bowl. When we pull it down, more water going to flow out. The reason is because when water tank(external) buttons are pressed, the slider will lock the water shutter and making the shutter harder to move down(close the output hole). If you adjust the slider higher and when water fills up, it floats higher. When it is higher, it goes down faster when water start to drained out to the toilet bowl and it unlocked the shutter part faster and making the shutter part able to move down faster to close the hole.

If the slider is adjusted lower, the shutter will be unlocked much slower and thus more water flowing out.

Generally, these 2 mechanisms are just to control water flowing out of the toilet bowl in different ways,

Water output differences between these 2 buttons are determined by the length of the rods and do not have anything to do with the water output canister.