The parts of a toilet include internal parts (filler valve, filler float, overflow tube, flush valve, siphon tube) and external parts (handle, tank, rim, bowl). While internal toilet parts create the siphon that makes a toilet work, the external toilet parts have a role as well beyond that of comfort and appearance.
Toilets flush when enough water is pushed into the siphon tube that it fills up. This amount of water causes the siphon action that sucks the water from the toilet bowl. The siphon process ends when the toilet bowl is empty and there is nothing left to pull.
What turns a primitive toilet bowl with a siphon into the common household toilet is the tank. Small amounts of water are not enough to cause the flush reaction because there is not enough water to fill the siphon tube. If there is not enough water in the tank, the siphon won't work, so the tank stores several gallons of water at a time and refills quickly. These several gallons of water are what make all the other toilet parts work together to create the siphon. The handle of the toilet is attached to the flush valve that acts as a plug in the tank. When the handle is pushed, the valve lifts and all the tank's water pours out into the bowl and down the siphon tube, filling it and causing the siphon to start. The other toilet part that is included in this process is the overflow tube. When the flush valve lifts, some of the tank water is siphoned up the overflow tube and directed to the bowl, to starts slowly refilling it. When the handle is released, the flush valve settles back into place and plugs the tank again.
To refill the tank and the bowl, the rest of the toilet parts mentioned above come into play. The filler float floats in the tank water and is attached to the filler valve. When the toilet's handle is pushed and the water leaves the tank, the float drops with the water level and, when it does, the filler valve is opened. While the toilet flushes, the refill valve starts slowly refilling the tank. Once the water level in the tank floats the filler float back to the top, the valve is shut off and the water stops running.
