The proper names of the two valves in a typical home toilet are the flapper valve and the ballcock valve. The flapper valve sends water from the tank to the bowl during the flushing of the toilet. The ballcock refills the tank and also sends a small amount of water to the bowl during the flush.
David, tercir is wrong. A flush valve is THE valve inside of a toilet tank that allows water to refill the tank when you flush your toilet. That flush valve has a float on it so when the tank refills to a certain point, the float shuts the water off. A flapper valve merely HOLDS the water in the tank until you flush the toilet. The flapper valve is the thing on the bottom (inside) of your tank that covers the water outlet. When you flush your toilet, that flapper raises the water that is currently inside of your tank, is what refills your toilet bowl when THAT water goes down into your sewer system. OK?
A flush valve (if you are talking about a toilet) is the flapper at the bottom of the tank. I suppose it could also be called a drop valve. At any rate, a flush valve is designed to rest in place preventing water from passing. When the flush valve is raised, trapped air in the bell of the flapper will cause it to float as high as possible, allowing water to pass without restriction. When the water level is low enough the flapper will float back down and seal the opening, thus allowing the tank to refill and be ready for another flush. Good luck. :)
