October 29


How Does a Toilet Flush Work?

By Robin Hatch

October 29, 2021

A toilet, loo, water closet, WC, lavatory, whatever you want to call it, is a ground-breaking piece of equipment. However, they’ve undoubtedly received improvements after improvements since the beginning of humanity.

From holes in the ground to the first flushable toilet in 1775, it has revolutionized how we dispose of wastewater. But not many people understand the concept behind this mechanism. So, how does a toilet flush work?

Because the toilet isn’t electrical, fundamental physics is key to a successful flush.

By pressing down a toilet handle, you initiate the flush. When this occurs, the rubber flapper (or float valve) is lifted, causing the stored water inside the toilet to fall through to the toilet bowl at a pressured rate.

The fill valve (ballcock) pressurizes water back into the cistern, ready for the next flush when the water is empty.

Considering it’s estimated that we use a toilet around four to ten times each day, we can easily forget how magnificent this piece of bathroom equipment is. Using simple physics can dispose of, refill, and maintain water levels to ensure an equal flush continuously.

If you’d like to become knowledgeable on a more in-depth version of the above, I recommend reading the below. Here we break down each step of a toilet flush from initiation to refilling the cistern.

Learn More About Your Bathroom Here

How A Toilet Flush Works

Almost everyone around the globe has access to a flush-operated toilet daily. Their used worldwide and will continue this way for the foreseeable future.

The toilets themselves are straightforward to manufacture, are durable, and aren’t significantly overpriced due to the materials used. However, you can quickly forget how complex this toiletry device is.

To better understand how a flush toilet works, see the below.

Parts Of A Toilet

Before we got into the step-by-step process, we thought it would be beneficial to talk about the parts behind making a toilet flush. Becoming familiar with these will undoubtedly make you understand the below much easier. 

Tank/cistern – This is pretty obvious but a vital part of the flushing system. The tank or commonly known as a cistern stores the water used to generate the flush.

Tank lever – When you initiate a flush, you’ll push or pull the tank lever (depending on how it’s positioned), and it’ll remove the flapper from its original position allowing water to flow through to the bowl.

Flush valve – To generate a powerful and effective flush, a flush valve is used to rush the water from the cistern to the bowl forcefully. This helps clear waste much more effectively.

Flapper/float value – As mentioned above, when the tank lever is pulled or pushed, it removes the flapper from its original position, releasing the water into the bowl.

Fill value/ballcock – The name gives this part away. As you can imagine, this fills the cistern back up with water after each flush.

Toilet bowl – Lastly, the toilet part where the waste gets flushed away.

Now you understand a brief overview of the components used to flush a toilet. It’ll make understanding the below step-by-step flushing process much more straightforward.

Flushing The Toilet


First is the initiation step of flushing a toilet. This is performed by pulling or pushing on the tank lever (usually located on the side of the cistern). Inside the cistern, the flapper or float valve is released from the seal when you initiate the lever. Your flush is now becoming active and will shortly push your waste into the drainage during this.

Open Flapper

Now the flapper is open; water can present itself in the bowl. However, it doesn’t just fall into the toilet, as there wouldn’t be enough pressure to flush away the waste.

Because of this, a flush valve is used. It’s a much more robust mechanism that releases large volumes of water when activated. Because pressure is built up inside the valve, water can come into the bowl quickly, causing the flush to be much more successful.


When the water from the cistern travels to the bowl, it equally spreads itself over manufactured holes for an even spread of coverage. The bowl itself was developed to reduce the occurrence of cleaning and improve the overall pressure generated to flush away the waste.


As the water comes down from the bowl’s rim and hits the water, it’s forced into something called the s-bend. An s-bend on a toilet is where the current water is before you flush the toilet and resembles the shape of an “S.”

Because a flush is a powerful flow of water, it forces the s-bend water levels to rise and remove the waste.

The purpose of the s-bend was to ensure that water is constantly present because as the pressure of the flush relaxes, water cannot overcome the upwards bend to fall into the drainage system.

Many people think this is for disposable purposes. However, it’s used to ensure no gasses become present in the toilet system from the sewage. If this were to occur, you’d receive an unpleasant smell which can sometimes be toxic.  


After the waste has overcome the s-bend, it flows its way to the toilet’s trap pipe. This is another prevention method to ensure gasses or waste doesn’t start smelling and potentially releasing harmful chemicals into your property.

When this reaches a certain pressure level, it’s then transferred to a drainage system that exports the waste away from your house and into the main sewage line.

Refill Cistern

While the above is occurring, the fill valve indicates that the cistern is empty. Because of this, pressured water then fills the cistern back up, so it’s ready for the next flush.

Although the above seems like a long process, this all happens in just a few seconds.

From the outside, a toilet seems like a straightforward bathroom appliance. However, underneath there’s a well-engineered and thought-about piece of ground-breaking equipment.

Next Steps

Learn more about toilets below.

Where Does Toilet Waste & Water Go? Learn Here

Does Toilet Paper Dissolve? Learn How Toilet Paper Works

Toilet Won’t Flush & It’s Not Clogged – How To Fix

After reading the above, you should now know how a toilet flush works. The process sounds relatively simple, but it’s far from that expectation. It’s an excellent bathroom appliance that is undoubtedly here to stay and will continue far into the future.

We’ve compiled a complete list of frequently asked bathroom questions for new and experienced homeowners.

Our experts answer these questions to help assist you through DIY projects and home repairs.

Now you understand the concept of a flushing toilet, will you be considering your plumbing from now on?

Robin Hatch

About the author

For over a decade, Robin has been a real estate agent, interior design specialist, and mother. Through her trials and tribulations, she wanted to create the perfect website to help you save money and make your home look beautiful.

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