How a Toilet Works - An Overview
A toilet has two major components, the tank and the bowl. The tank stores a charge of water to flush out the bowl. A toilet works when you press the handle, the stopper in the bottom of the tank opens and allows the water to quickly drain out and flush the bowl.
As the water from the tank enters the bowl, it overflows and the excess water runs out the bottom of the bowl and into the drain line. This slug of water creates a siphon as it goes down the drain line and pulls the contents of the bowl with it. The siphoning continues until there is no more water and air enters the drain. The air breaks the siphon and now any more water that enters the bowl, refills it.
If too little water is used to flush out the bowl, little or no siphoning occurs and the bowl is not purged. If the water from the tank enters too slowly, the water runs down the drain but there isn't enough at one time to start a siphon. Therefore, to flush out the bowl completely, there must be enough water and it must pour in suddenly.
When most of the water drains from the tank, the stopper drops back into place and the tank begins to refill, along with the bowl. The water level rises inside the tank until it reaches the float and lifts it high enough to shut off the fill valve. The next time the toilet is flushed, the water drains out, the float drops down and the fill valve opens and starts water flowing into the tank.
Because low flow toilets use less water, the pressure generated by gravity may be too low to purge the bowl. The force of the water is increased with a jet assist device. The jet assist blasts the water through the bowl, cleaning it while using less water.