The Flush Mechanism
The purpose of the tank is to act like the bucket of water described in the previous section. You have to get enough water into the bowl fast enough to activate the siphon. If you tried to do that using a normal house water pipe, water would not come in fast enough -- the siphon would never start. So the tank acts as a capacitor. It holds several gallons of water, which it takes perhaps 30 to 60 seconds to accumulate. When you flush, all of the water in the tank is dumped into the bowl in about three seconds -- the equivalent of pouring in a bucket of water.
There is a chain attached to the handle on the side of the tank. When you push on the handle, it pulls the chain, which is connected to the flush valve. The chain lifts the flush valve, which then floats out of the way, revealing a 2- to 3-inch (5.08- to 7.62-cm) diameter drain hole. Uncovering this hole allows the water to enter the bowl. In most toilets, the bowl has been molded so that the water enters the rim, and some of it drains out through holes in the rim. A good portion of the water flows down to a larger hole at the bottom of the bowl. This hole is known as the siphon jet. It releases most of the water directly into the siphon tube. Because all of the water in the bowl enters the tank in about three seconds, it is enough to fill and activate the siphon effect, and all of the water and waste in the bowl is sucked out.