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How Does a Toilet Flush Work? – Everything You Should Know!

how does toilet flush work
Written by Kai Michel
Last Update: August 10, 2023

Toilets have become so common and entangled with our lifestyle that most of us take them for granted. They do save lives by stopping deadly diseases, but for that reason a toilet needs to stay clean and hygienic. Flush system toilets use a water stream to clear out the discharges.

If you want to keep your flush toilet clean, you’ll need to maintain it regularly. However, that may become an issue if you have no basic idea of how the system works. That’s where we come in.

Our today’s guide has been crafted to answer the question: “How does a toilet flush work?” We’ll break down the anatomy of a toilet, exploring how the flush mechanism works, how the tank gets refilled, and what the siphon does.

If you’re curious to know, follow along.

How Does a Toilet Flush Work? – The Anatomy of a Toilet Flush System

Toilets are made of two compartments –

The bowl– this drains directly to the siphon, and it serves as the toilet seat.

The tank– this is attached to the wall that looks like the backrest of a chair. Attached to it is the flush handle. It has the following parts: the flush valve, fill valve, flapper, and the overflow tube.

Now the question is, how does a toilet flush work? When you trigger the flush mechanism by pressing the switch, what really happens inside?

  • Once you press the flush button, you pull a chain that is designed to release the water in the tank directly to the bowl by raising the flapper.
  • And once that is done, the dirty water is then drained from the bowl siphon.
  • Once you have an empty tank, the toilet flapper will shut itself automatically while the fill valve starts working.
  • The fill valve will help replace the water in the tank. It conveys water via the refile tube and transfers it back to the overflow tube.
  • While the fill valve is still working, the water increases the same time with the water in the tank. Once the water in the tank gets to the fill line, the valve goes off automatically; this stops the system from flushing.

The Bowl Siphon

The Bowl Siphon

You can flush your toilet in the absence of the tank component. Does this sound strange to you? Well, all you need to do is allow more water goes up the siphon. For instance, in the absence of a toilet tank, the bowl can still carry waste to the sewer.

Though tanks contribute to the flushing process, the main trigger is the siphon. On rare occasions, does the use of toilet handle, and the tank facility the entire process.

If it’s difficult to imagine the possibility of flushing a toilet in the absence toilet’s water tank, then carry out this experiment and see the outcome.

Empty a bucket of water directly in the toilet’s bowl and observe how the water level in the bowl increases. Adding water to the bowl will increase the water level above the siphon.  The water in the bowl will maintain an average limit regardless of how often you repeat the process. The siphon is designed to control the amount of water the toilet bowl can store.

Try something different. Empty the water in a cooking pot directly to the bowl of your toilet and then observe the outcome. This will lead to a blown flush without the pull of a handle.

Once this occurs, the tube linked to the siphon will be filled with air and will produce a flushing sound as a result.

The Flush Mechanism

The Flush Mechanism

Similar to the water pot experience you had, flushing a toilet is possible in the absence of the tank. You can also flush in the absence of a running tap; you will need a few gallons of water to carry this out.

Although the process can get a bit tiring if you need to fill the bowl on each trip to your bathroom. As to this effect, toilets are designed with tanks; and these tanks are meant to function as water pots; they gather, store, and send water, saving you the stress of going up and down.

Once most people learn about the process of flushing, often they have one question in mind: why are the tanks always big?  Why is it not designed in the size of a faucet?

Well, the answer to all of this is no. The spout that runs water with a similar volume to that of a sink will produce enough pressure and speed that is enough to get the toilet’s siphon active.

The purpose of a toilet tank is to help store water and drop it when needed directly in the toilet pot once the flush handle is pulled. Once the handle is pulled, all the waste matter disappears magically within a few seconds.

Often, people tend to deal with the handle of the tank, which shares a direct connection with a chain inside that has a link to the flush valve.

Once you pull the handle, you tug the chain at the same time, and as a result, the valve gets opened. Opening the valve will create a hole that has an approximate diameter of three to four inches. Water gets to the bowl through this hole.

Afterwards, the water gets down to the rim, and the siphon jet flushing away all waste matter at the same time. Due to the pressure and the speed, the siphon located in the toilet gets activated immediately. This action is similar when compared to flushing, using a bucket of water.

The Refill Mechanism

Toilet Refill Mechanism

Flush is possible once you have enough water to trigger the toilet siphon. The function of the tank is to transfer enough water (approximately) two gallons. The water gets across the bowl in 20 to 30 seconds and carries out flush once the handle is pulled.

Now the supply of water is drained, the valve connected to the flush handle get shut automatically; this will give room for more supply of water to aid the next flush. At this point, the mechanism for refill performs the action.

The toilet refill mechanism is designed with a valve that will help activate the water supply. A float ball is used to signify the process. The ball drops once the tank is totally empty, and it rises again once the tank is refilled. During this, water is forced to get through each overflow tube directly to the bowl.

The float ball or the valve filler works in tandem with the toilet’s overflow tube during a flush process to maintain the water level. The float ball notifies the fill valve when to stop or start loading more water.

On the other hand, the over follow tube is known to direct water once it gets to its gauge in the right direction. If the float ball has issues, the toilet overflow tube will be forced to redirect excess water to the bowl; this will lead to an over float tank.

If you are experiencing an unending flush, then this is possibly one of the issues you’re encounter.


1. How does a toilet tank work?

Ans. The function of the toilet tank is to hold back enough water to flush the toilet. Once the handle is pulled, the tank supplies the water needed and rushes it down via an opening located below. The opening has a straight connection with the bowl; this opening allows water to travel from the tank to the bowl and finally triggers the flushing effect.

2. Are all new toilets low flow?

Ans. The contemporary models are designed to flow slowly. Usually, the tanks are built to use an average of 1.6 gallons while flushing, although most modern designs are enhanced with more efficiency.

3. How do I know if my toilet is low flow?

Ans. Check out a flush volume that is placed in-between the tank and the seat. If the volume is 1.7 gpf or 1.30gpf, then the toilet is a low flow model. Take the lid off and check out the flush volume data stamp or volume stamp that is located within the tank. The stamp can sometimes be located on the lid or on the wall of your tank.

About the author

Kai Michel

Hello, this is Kai, addressing homeowners in need of some help with their home renovation projects. I’ve worked on numerous toilet repair projects over the years that incorporated a wide variety of tasks, from repair to renovation and maintenance. Besides acquiring a degree on the legal codes and procedures, I gathered vast insights into bathroom settings, toilets, showers, fittings, and other household appliances, fixtures, and components. This helps me guide my clients through their home improvement and interior development plans. Since maintenance is my area of expertise, I can assist people in all phases of the actual ‘improvement’ process. To get my messages even further, I contribute to this site through my blog posts. Check my content here for expert suggestions!

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