# How a Toilet Flush Works

How a toilet flush works with no motor or pump, using gravity, a rubber flapper and a curved siphon pipe to empty the bowl and refill the tank\.

By bapt

Topic: Machines

[Open the interactive Jig](https://ask.jig.com/j/dwcrrWdhPEah)

## Transcript

### 1. How a toilet flush works

Press a handle and everything in the bowl disappears in seconds\. There is no motor and no pump inside\. Just gravity, a rubber plug and a cleverly curved pipe\. Drag the room to look around\.

A modern toilet uses about 4\.8 litres \(1\.28 gallons\) per flush\. Older ones used up to 13 litres\.

### 2. Look inside

Let us slice the toilet in half\. On top sits the tank, a store of clean water waiting for the flush\. Below is the bowl, and hidden in the china behind it is a curved pipe called the trapway\.

The highlighted S\-shaped pipe is the trapway\. It leads to the drain in the floor\.

### 3. Water that waits

At rest, a rubber plug called the flapper covers a hole in the bottom of the tank\. The weight of the water above presses it shut\. In the bowl, water fills the bottom of the trapway and makes a water seal that keeps smelly drain air out of the room\.

The hole under the flapper is about 7\.5 cm \(3 inches\) across\.

### 4. Press the handle

The handle turns a lever inside the tank\. The lever pulls a little chain, and the chain lifts the flapper\. Now the tank water can rush out of the hole into the bowl\. Press Flush, or press the chrome handle itself\.

The tank empties in only about 3 seconds\.

### 5. Rim and jet

The falling water runs into a hollow channel under the rim\. Small holes let it wash down the sides of the bowl\. Some water also races down a hidden passage to a jet at the bottom, which squirts straight into the trapway\.

The jet is what starts the siphon quickly\.

### 6. The siphon

Water spills over the top of the trapway bend and fills the pipe completely\. As that pipe full of water falls toward the drain, it pulls the bowl empty behind it\. This pulling flow is called a siphon\. When air finally gets in, the siphon breaks with a gurgle\.

The gurgle at the end is the sound of air breaking the siphon\.

### 7. Refill

With the tank nearly empty, the flapper floats down and seals the hole again\. The float, a hollow cup, sinks with the water and opens the fill valve\. Fresh water from the supply pipe pours in, and a thin tube trickles some into the bowl to rebuild the water seal\.

The thin refill tube sends its water down the overflow tube and into the bowl\.

### 8. Ready again

As the tank fills, the float rises and shuts the fill valve at the right level\. If the valve ever got stuck open, the extra water would spill down the overflow tube into the bowl, not onto the floor\. Every part is ready for the next flush\.

A whole flush cycle uses only gravity and the pressure of the water supply\.