Repairing a Noisy Toilet
There are only a few parts inside the toilet, but when they’re not working correctly, they can cost you a lot of wasted water and money. Understanding how the toilet works makes correcting the problem easier. When the flush handle is depressed, a large, air-filled rubber plug (the flapper) at the bottom of the toilet tank is raised. This allows water to rapidly escape out of the tank into to toilet bowl.
The rushing water enters the bowl through many small holes at the underside of the rim and through a large port at the bottom of the bowl. The water from the ports creates a washing action that is intended to clean the bowl. As the wash water begins to fill the bowl, its own weight forces it downward to an "S" shaped port (the "P" trap) hidden in the base of the toilet.
Second Phase of the Flush
The action of the water filling the P trap causes a siphon to begin within it. The siphon, which is the second phase of the flush, becomes so great that it rapidly draws the water out of the bowl and into the sewer. The third part of the flush is the accumulation of fresh water that remains after the siphon action has removed the waste. This modest amount of water is needed to keep the P trap full. Without water in the P trap, sewer gasses could back up into the bathroom.
Note: There are no moving parts between the flapper in the toilet tank and the sewer lines. A flush depends entirely on the forces of gravity and siphon.