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How Does A Toilet Work?

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

There are few items in our home that we genuinely would be upset about should they go.

Sure, there are a few that have emotional or physical value, but let’s face it, most of the items in our house are basically garbage to anyone but ourselves.

Nobody needs 10 allen keys that are all the same size, or that superglue that dried on the cap and now no one can open.

However, while losing these items would upset us for a day or two, losing some things in the house would be truly upsetting.

Imagine suddenly finding out you don’t have a fridge or toilet anymore?

So, we cherish these items in more than just a sentimental way, but were I to ask you how exactly they work, you would probably falter.

Like toilets (see also ‘What Are Toilets Made Of?‘), how do they work? Is it magic? Or just well-designed craftsmanship?

Well, put your plumbing cap on, for we are about to give enough information on toilets to give a professional a run for his money, as we inform you exactly how a toilet works.

History Of The Toilet

The history of toilets is as old as the history of human’s pooping.

For as long as we have been able to, we have tried to find a nice, quiet, safe place to take care of business.

The toilet, or at least the idea of a place to dispose of our waste, has been around for a long time, dating back to the Stone Age.

The Sumerians, the Indus valley civilization, Skara Brae, all these places have latrine like areas to dispose of waste, but it was the ancient Romans who are credited with the first known toilet with waste disposable, which consisted of a hole in a seat in a bathhouse.

This seat and hole was connected to an indented runway along the ground, so when the toilet was periodically flushed, the waste would go into this runway and away from the room.

During the medieval period, most toilets were either cesspits, privy rooms, chamber pots, or holes in various areas instead of actual latrines.

It was until the Tudor period in England, that toilets began to resemble modern equivalents.

In 1596, Sir John Harington wrote about a type of toilet that had a water tank on top which, when the flush lever was pulled, would release a stream of water and flush away the contents of the bowl.

This is perceived to be the first flush toilet and from this humble beginning, the designs and ideas behind the flush toilet became more varied and complex, until we got our modern flush toilets today.

How Does A Toilet Work?

The toilet can flush (see also ‘What Is Automatic Toilet Flusher And How Does It Work?‘) thanks to gravity and a vast amount of water.

After you have finished your business, you will stand up, either put the lid down or keep it up, and activate the flush feature – whether that be pushing a button or pulling a handle.

As you pull the handle, you start an effect known as the siphon effect. This is when two contained areas are connected with a pipe, with one contained area being lower than the other.

The upper contained area (or container) is filled with water, and each area has an end of the pipe in it.

The pipe goes upwards from the water filled area until it is at a higher elevation and curves downwards sharply into the other area.

This is known as a siphon. When you place the ends of the pipe in both containers, nothing will happen because they are filled with air.

However, if you create a vacuum (i.e. remove the air from one end of the pipe) in the pipe end of the lower container, then the air pressure pushing down on the water in the upper container will force the water through the pipe and out the other end.

Vacuums can be created in many ways – like sucking on one end of the pipe – but in a toilet it is done with the flush handle.

The flush will force air out of the siphon and allow the water to leave the tank.

The air pressure will push down on the water until the tank is empty, forcing it into the bowl.

When the flush is finished and all the water is gone from the tank, the air will replace the lost air in the siphon.

The tank will then refill with water, which is contained by the air now in the siphon, thus being ready for the process to start again.

Parts Of A Toilet

As with much of the home’s infrastructure, toilets have evolved with time.

From holes in the ground to pots on the floor, toilets have come a long way.

Now, as a modern day toilet user, you have a few more options available to you.

Like other appliances and tools in the home, toilets are made up of parts that work together to make them efficient.

However, as with every tool, every part requires a littler explanation to understand them completely:

How does a toilet work?

1. The Toilet Handle

The handle is what you twist (or sometimes a button you push) to send water to the bowl through the flushing mechanism.

The handle is also where the water supply is attached to the tank and drain valves.

The handle is attached to the lift chain with a chain that runs through a hole in the bottom of the toilet tank.

This hole is not visible to the user of the toilet, but is visible when you peer into the top of the tank. By pulling the handle, the user will initiate the flush procedure.

2. The Lift Chain

The lift chain is what controls the flow of water from the toilet tank to the bowl.

This is seen by the user and is housed inside the toilet bowl.

The lift chain is attached to the toilet handle with a chain that runs through a hole in the bottom of the toilet tank.

The chain is attached to the mechanism on the bottom of the toilet tank that triggers a flow of water from the tank to the bowl from the toilet’s hole.

The chain is also attached to a mechanism that is attached to the toilet’s handle. This mechanism triggers the water supply valve on the toilet handle.

3. The Toilet Flapper

The toilet flapper is what controls the flow of water in and out of the toilet tank and the bowl by opening and closing the valve that allows water to pass through the rubber seal at the bottom of the tank.

This little object sits on the flush valve itself and creates the seal to prevent water going through.

The toilet flapper is connected to the lift chain, and this chain also connects the toilet flapper to the toilet handle with said chain.

When the toilet is flushed, the lift chain lifts the toilet flapper up, breaking the seal created, and allowing water to enter the bowl.

When the flush is complete, the tank will become empty and the flapper will re-assume its position to create the seal once more.

4. The Toilet Flush Valve

The toilet flush valve is what controls the flow of water from the toilet tank to the toilet bowl, and it sits at the bottom of the toilet tank.

When the flush is engaged, the flapper will be lifted off by the lift chain and an opening will be created in this valve to allow water to pass through.

A flush valve’s size will dictate how much water will be released into the bowl and how fast.

A larger flush valve will release much more water quickly, whereas a smaller valve will release less over a longer period.

Most flush valves are about 2 to 4 inches in diameter, but some toilets now have two flush options, one to open the smaller flush valve and one to open the larger flush valve, thus giving you a nice choice.

5. The Toilet Tank To Bowl Gasket

The toilet tank to bowl gasket is what seals the outside of the toilet tank at the point where the toilet flush valve is.

The tank to bowl gasket is a ring that is placed on the outside of this opening and seals the outside.

Unlike a flapper, though, it doesn’t move and must remain sealed and closed at all times.

Without this rubber seal, water would be constantly leaking from your tank and every time you flushed a wave of water would likely leak out of this area, instead of into the bowl.

If you are noticing leaks around the tank, check this area first. Rubber is a resilient material, but it will wear over time, and you may need to replace the toilet tank to bowl gasket.

6. The Toilet Bowl

The toilet bowls are the main part of the toilet we all interact with. They are the part you sit on to go to the bathroom.

The toilet bowl is connected to every part of the process: the toilet tank, toilet flapper, toilet float, toilet fill valve, trap assembly, bowl gasket, and so on.

Toilet bowls are either circular or ovoid in shape with the front occasionally being elongated as well.

It is a mostly empty bowl that is connected to a pipe at the bottom with water in it.

Toilet bowls in general will be made of either ceramic or plastic, as these materials are unlikely to break easily and are much easier to clean than other materials.

In the toilet bowl, there is one large opening at the back and many smaller ones around the rim under a lip of ceramic or plastic material.

When we flush the toilet, 80% of the water comes out of the larger opening to push our waste down the pipe and is forced into the sewers connected to our houses.

How does a toilet work?

The other 20% of the water comes out of these little holes. This 20% is for cleaning the entirety of the bowl of filth.

The toilet bowl is also the area where the seat rests upon, and the lid can be closed.

Once the flushing is complete, water will stop coming through the holes in the bowl and the bowl will be clear, excluding the water at the bottom.

7. The Toilet Trap

The toilet trap is the area at the bottom of the toilet bowl, specifically the pipe that connects to the bowl.

The part we see of the toilet trap is the small puddle at the bottom of the bowl in what looks like a pipe.

This is just a small part of the trap, with the actual trap being this pipe reaching up and around in a U-bend shape.

The reason for the U-bend is once again to create the siphon effect to move the contents of the bowl into the sewers.

However, unlike before, air pressure is not that much of a factor.

The sheer force of the water traveling down from the tank pushes the waste and water through the pipe and upwards, getting over the U-bend and being deposited into the sewer.

Once the force of the water stops and water is no longer traveling through the pipe, the air will fill the space once again and the water that wasn’t pushed up the pipe will settle at the bottom of the bowl.

Baring the transit of waste into the sewers, a toilet trap has two functions. The first is the stopping of sewer gas.

The water at the bottom of the toilet bowl actually acts as a barrier, preventing any smell or gas from coming up the pipe.

It may not be the most deadly thing in the world, but you also don’t want your house to smell like a sewer (see also ‘The Reason Your House Smells Like Sewer When It Rains‘).

The second function is that the toilet trap can catch things that may clog your toilet or the sewer.

When you flush waste and toilet paper is it light enough and can decompose fairly easily, therefore water will easily carry it away.

But other objects that don’t decompose well, will be caught in the toilet trap instead, due to their durability and weight.

This may seem bad, but it is much easier to unclog something from your toilet (see our guide to unclogging your toilet) trap with it being a few feet of pipe, rather than pipes much further down.

8. The Toilet Fill Valve

This valve is very similar to the toilet flush valve, except that its function is the exact opposite.

Whereas the flush valve lets water out of the tank, the fill valve lets water into the tank.

This valve is connected to the main water supply line for the toilet and once the toilet tank has been activated for a flush, the water will decrease in the tank.

Once the toilet float activates, the fill valve will open and begin refilling the toilet.

Once the float has assumed its normal position, it will close and stop refilling the tank.

9. The Toilet Float

Like the fill valve is a parallel to the flush valve, the toilet float is a parallel to the toilet float.

This float is normally a plastic ball, cup, or cylinder float that is filled with air.

Its entire purpose is to regulate the water levels of the tank, which – depending on the level – will make it open the fill valve.

Before flushing is engaged, the water level will be at its highest. During these moments, the float will float at the top of the tank and so the fill valve will be closed.

When the toilet is flushed, the water level will drop and so to will the float.

The float’s attachment to the valve means that once the float falls to a certain depth in the tank – thanks to the water leaving -, the fill valve will be pulled open.

As the water increases in the tank, the float will reach the top of the tank again and the fill valve will close.

10. The Refill Tube

The refill tube is the small black tube that is connected to the fill valve.

While its purpose might not be apparent immediately, it does have an important function.

It connects from the fill valve to the overflow pipe, which goes through to the bowl of the toilet.

When the toilet tank is refilling, this tube will send water from the tank into the bottom of the bowl.

This way you refill the small amount of water in the toilet trap and prevent nasty smells coming up from the sewer.

This tube’s function is quite literally what we have said here and has very little to do with the overflow pipe beyond that.

11. The Overflow Tube

This tube is one that sits in your toilet tank, somehow inconspicuously and suspiciously at the same time.

However, this is one of the most important features of your bathroom.

This large tube prevents your bathroom from flooding by managing the overflow potential of your tank.

When the water in your tank rises above a certain level, it will come into contact with the overflow tube.

How does a toilet work?

At this point, the overflow tube will begin sending water from your overflowing tank into your toilet, thus preventing a catastrophe.

When your toilet is having problems managing its water, you will thank your lucky stars for one of these bad boys. It is one of the best fail safes.

The normal water level in the tank should be about ½ an inch to a full inch below the overflow tube.

If you are continually finding your overflow tube being used or required to keep your toilet from overflowing, contact a plumber as you may have a problem.

12. The Toilet / Tank Lid

This is normally a flat, rectangular lid with lips on the side, that sits on top of the tank or cistern and is held in place by gravity.

This is actually one of the most necessary components to the toilet. It allows the users of a toilet to access the tank, while also keeping things out of said tank.

You may think it doesn’t matter if a bit of dirt or material gets into the tank, but you, my friend, would be dead wrong.

Clean water is necessary to keep all parts of the toilet moving and to keep it functional.

Dirt can become trapped in valves, preventing them from filling and flushing, it can become attached to the float or the flapper, stopping them from opening or floating, and it can even become stuck in the pipes causing blockages.

The other thing about dirt is that it inevitably brings bacteria along with it. These bacteria can remain in the tank or pipes and begin reproducing.

These bacteria will start to multiple and could clog up parts of the toilet or make the whole system incredibly unsanitary. Therefore, a lid is a must.

13. The Wax Ring

The wax ring works a bit like the toilet tank to bowl gasket, but it keeps out much more harmful things than the gasket.

See, the ring is placed between the bottom of the toilet and the pipe in the hole that leads to the drainpipe – called the toilet flange.

This ring acts as a very strong seal that stops anything that goes through or could come through the drainage pipe entering into the bathroom.

The main things it keeps out are the flushed waste and water that you send down the drainpipe, and the water and gasses in the sewer from coming back into your bathroom.

While a wax ring is a bit annoying to install, it is necessary and one of the things that must be in your bathroom before you start flushing your toilet.

14. The Toilet Flange             

A toilet flange – or a closet flange – is a type of pipe fitting that is screwed into the bathroom floor.

It connects the toilet’s bottom to the drainpipe, which leads into the sewers. It is one of the most important connective pieces of the toilet.

Due to the flange being in constant use – it has water and waste pumped through it constantly – it is necessary to test and check it every once in a while. It can be prone to breaking or wearing away.

If your toilet is starting to wobble (see also ‘ How To Fix A Wobbly Toilet In Five Easy Ways ‘), there is leaking at the base of the toilet, or a horrible smell is permeating your bathroom, it is time to replace the flange.

15. The Toilet Bolts

These are the bolts that are used in the flange to connect it to the bathroom floor.

This makes sure that your toilet is nice and secure with no worries of it collapsing or wobbling.

Normally, there are four bolts that enter through the top of the flange into the floor.

Should your toilet be wobbling or moving, then check that the bolts are fine and that the thread that they have made in the flange is not wearing out.

16. The Shut-Off Valve

The toilet shut off valve is connected to the main water supply line that comes out of the wall of the bathroom and connects to the toilet’s tank.

How does a toilet work?

This valve is incredibly important for toilet maintenance and repair, as it provides a quick and easy way to shut off all water to the toilet, without cutting out water flow to the rest of the house.

So, to turn off the flow of water to the toilet, turn the valve clockwise, and to turn it back on, turn the valve counterclockwise.

Normally, the valve can be turned using a flat headed screwdriver.

17. The Water Supply Line

The water supply line is the pipe in which water flows into your tank. Without this, your toilet wouldn’t have water, and you would be unable to use the toilet as designed.

This line is normally stainless steel and goes from the shut-off valve to the fill valve in the tank.

Problems with the supply line affect the whole toilet and potentially the rest of your bathroom as well, so make sure to check on it regularly.

Common Problems With Toilets

No matter how well-crafted they are, toilets – as with most things in life – will experience problems and breakages.

However, if you know what they are, you can predict and prevent them:

Low Water Level

Most toilets have a certain amount of water at the bottom of the bowl and in the tank.

If you have a low water level in either of these, then you may have to take a closer look.

The most common reasons for low water in the bowl are: the refill tube being disconnected to the overflow tube, the fill valve is not filling the tank properly, and the toilet bowl being cracked and leaking.

If the water level is low in the tank, then the most probable causes are: malfunctioning fill and/or flush tubes, a leak in the water supply line, the float not doing its job, and a crack or leak in the tank.

Wobbly Toilet

If your toilet is wobbling, then the culprit is most likely the toilet flange.

This is the foundation of the toilet and holds it in place.

Normally, it means that the bolts holding everything together have come loose or that the flange and the wax ring have worn away through time and use.

If you are having this problem, it is best to speak to a professional unless you have necessary plumbing experience.

Too Much Water

If your toilet is constantly relying on the overflow tube or is overflowing itself, then the valves are probably your problems.

You have either a defective fill or flapper valve that doesn’t close properly, or a float that has been positioned wrong or it doesn’t float properly.

These parts are normally cheap and easy to replace, so you shouldn’t have a problem with them. Just make sure to turn off the water before you do anything. 

How Much Water Does A Toilet Use?

About two gallons of water for every flush. That’s a lot of water, but it’s only enough for a couple seconds of work.

Of course, the water used by a toilet would be much larger if we used the traditional method of doing our business.


Toilets are tricky business, and you wouldn’t think that they would be so complex just to look at them.

However, they are made up of many different moving parts and have to constantly use and deal with one of the most common causes of erosion and corrosion in the world: water.

As such, always keep an eye on your toilet and know intricately what part does what in them.

It may save you time and a lot of money if you realize that the problem can be something you can solve yourself, instead of calling a plumber.

author avatar
Anthony Barnes
Anthony Barnes is the founder of Water Heater Hub and a second-generation plumber by profession. Before developing Water Heater Hub, Anthony Barnes was a full-time plumber, and he has undertaken a wide variety of projects over the decades. As a second-generation plumber, it was easy for Anthony to get used to the technicalities of all from a tender age


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Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases. When it comes to dealing with clogged drains, many homeowners turn