Flushing toilets use gravity and an increase in the height of water in the bowl when the user activates the flush valve to move water and waste through an "S-bend" into a drain pipe and out of the home. These simple devices have relatively few moving parts and, in most cases, offer many years of trouble-free service.
The S-bend serves two important purposes in the modern toilet. It is a water trap that prevents sewer gases from escaping back into the home. The increase in water level causes it to create a siphon to remove waste. The tank at the top of the toilet stores water for the flush. Activating the flush lever lifts a flapper valve to allow the designated amount of water to flow into the bowl to begin the flushing action. Holes, located under the toilet rim, allow the water to flow into the bowl while rinsing its sides. Once the level in the bowl is greater than that at the top of the S-bend, gravity begins the siphon, which quickly empties the bowl of its contents. Emptying the tank closes the flapper valve and causes a float valve to drop. This valve allows clean water to fill the tank and return the level in the bowl and S-bend to normal. Once the water level in the tank returns the float valve to its preset level, the water flow stops and the toilet is ready for the next flush.