Here you can see the internal workings of a toilet. When the handle is pushed down it releases the flush valve which allows for the water to drain into the toilet bowl. The flush toilet pictured then pushes waste up and over the inverted U shaped hill and then proceeds to block the opening with water. It is the difference in pressure between a filled bowl and the empty pipe shoves the water over the top. It is the attraction between the water molecules that keep the flow moving and eventually draining the bowl. Finally, after the water has been sucked out of the bowl, the tank and bowl refill. When the tank water level lowers, the float inside does as well. When it reaches the bottom the refill device is activated, which sends water into the tank and also into the toilet bowl. More water is sent to the tank until it is refilled. When the float reaches a certain height the tank stops filling.