WCs can all look alike actually they can be of two different types:
At fall , they are cleaned by the water that comes down from the water storage tank
with aspiration , a particular siphon placed inside them creates a venturi effect, a suction that makes the water flow faster by increasing the cleaning power li >
The trays where water is collected can be of two types:
a bell , where a heavy cast iron bell closes the water supply
to direct action , where the seal is given by a plunger on which a seal is mounted
Of this last type you can find models to be walled in the thickness of the masonry or external to be mounted on the wall behind the toilet.
It may happen that the WC water collection tray suddenly becomes noisy.
This can happen because the silencer pipe on the filler cock has come off or broken.
It will be sufficient to reposition it or replace it to solve the problem.