When draining water, pull the drain knob, and the knob pulls the water out through the lever. So that the water in the water tank will be released. After the water comes out, the water outlet plug falls and blocks the water outlet. At this time, because the water surface drops, the floating ball is also at the bottom of the water tank. The falling of the floating ball drives the lever to block the water from entering the water tank. As the water level rises, the floating ball will gradually increase due to buoyancy until the water inlet plug is pressed down by the lever to block the water inlet. In this way, the water tank is full of water.

When the water inlet pipe leaks due to a fault (for example, the water inlet plug cannot block the water inlet or the water inlet pipe is broken), the water level in the water tank will continue to rise and eventually overflow the water tank. The installation of seepage pipe solved this problem. When the water level rises to the seepage pipe, water will flow into the toilet from the seepage pipe, and water will not overflow the water tank. When the water inlet pipe works normally, the water level in the water tank will not reach the seepage nozzle, so there is no need to worry about the water flowing away.

The main mechanical principles used in toilet design include Archimedes principle, moment balance, Bernoulli equation and so on.