Toilets have two main parts: a tank and a bowl. The tank, which houses all the working parts, is where various types of toilets differ the most. Several different types of mechanisms are used to accomplish a toilet's basic operation--to flood the bowl with enough water to flush waste down the drain and then refill the tank and bowl with fresh water.
Here is how the most common mechanism works. When you flush the toilet, the handle lifts and a stopper, called the flush valve, releases the water from the tank into the toilet bowl. The resulting water pressure forces the contents of the bowl into the drainpipe.
As the tank empties, a float ball that had been floating on the top of the tank water drops. This activates a ball cock or water valve, which opens a water-supply valve that refills the tank. (Some toilets do not have the float ball and work through water pressure.) As the water fills the tank, the ball floats back up, and when the water reaches the right height in the tank, the it shuts off the valve.
A bend in the pipe just below the toilet serves as a water-filled trap that blocks the rise of sewer gases. Waste drains to a municipal sewer or to a septic tank.
Almost one third of a household's water is flushed down the drain. Older toilets use from five to seven gallons of water; newer toilets use only one or two. Some communities offer rebate programs if you replace your toilet with a more efficient model.