When a properly functioning toilet is sitting undisturbed, the water in the tank keeps the float held aloft. In this position, the ballcock (or fill valve) is held closed, preventing more water from entering the tank from the plumbing supply. Meanwhile, the flapper sits in the flush valve seat, preventing water from exiting the tank into the bowl.
Water in the bowl sits at a level in line with the weir, a dam-like structure in the trap that allows water to pass over it when the water level rises.
Once the flush handle is pressed, a lever and chain raise the flapper, allowing water to rapidly leave the tank and enter the rim of the bowl. The flapper is buoyant, which keeps the valve open while the water drains. Once the tank is empty, the flapper settles back into place.
The water from the tank travels around the rim, then down the siphon jet. On its way to the siphon jet, some of the water exits instead through slanted rim holes, washing the inside of the bowl and helping to send the water into a spiral.
The water travelling through the siphon jet fills the trap rapidly. Gravity takes over from there, creating a siphon, which pulls the water through the trap and out of the bowl, into the plumbing and out of the house.
The float lowers with the water level in the emptying tank. This causes the tank’s fill valve to open, allowing water to enter the tank from the plumbing supply line. A small amount of this water is diverted into the fill valve overflow tube, helping to refill the bowl.
As the new water enters the tank, the water level again rises, lifting the float. Once the float is at the appropriate height, the tank’s fill valve closes, and the toilet is ready for another flush.