How does a toilet work?

Toilet function is based on gravity and siphoning. If you were to add water slowly to the toilet bowl, you would find that the bowl would fill to a certain level, and then stop filling, the balance of the water you add going down the drain. If, however, you take a five gallon bucket full of water and quickly pour it into the bowl, what happens is that the suction of the water flowing out of the toilet literally pulls, or siphons, the water out of the bowl, leaving only a small amount of water behind.

When you flush a toilet by pushing the flush handle (or button in some toilets), the flapper chain or similar linkage pulls up on the flapper, breaking its seal with the flapper seat, allowing the water from the toilet tank to drain quickly through the flapper seat and into the toilet bowl. The flapper, once lifted from its seat, remains open by design until the tank is empty or nearly so.

Many toilets are designed to have the water enter the toilet bowl through a series of small holes under the porcelain seat rim. These holes are angled slightly, causing the water in the bowl to swirl around. This swirling action, combined with the speed of the entering water, causes the contents of the bowl to quickly and thoroughly exit from the base of the bowl, into the waste pipes, and, hopefully, out of your life forever. Some modern toilets use variations on this theme, some attempting to accomplish the same task with less water. Some even use the pressure in your water line to accelerate the flushing action.

The inlet valve float drops as the water level in the tank falls. After about an inch of drop, the inlet valve automatically opens, and fresh water flows into the toilet tank. A few moments later, when the water has drained sufficiently from the tank, the flapper drops back onto the flapper seat. That's right... for a few moments, the toilet tank is filling and emptying simultaneously. But it drains so much faster than it fills that the process works anyway!

The inlet valve will remain open until the water in the tank reaches a predetermined level. As the water height approaches this level, the upward movement of the inlet valve float closes the inlet valve. The toilet is now ready for another use.

During the flush, the siphoning action almost completely empties the bowl. The inlet valve is designed to divert a trickle of water through the overfill tube into the bowl as the tank is filling. Without this additional water in the bowl at the end of the flushing cycle, insufficient swirling action could occur at the next flush, and the toilet may even overflow if there was enough solid waste in the bowl!

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