How to fix toilet trap

The pipe which serves the toilet is called the soil pipe and is 3-4 in. (75-100 mm) in diameter. Other drainpipes for household fixtures are 1.5-2 in. (3850 mm) in diameter. The connection to each fixture must have a trap, which is a special U-shaped or P shaped fitting that allows the easy flow of water but retains a small amount in the bend to prevent noxious sewer gases from seeping up through the drains nto the atmosphere in the house.

The only exception is the toilets; they are all manufactured with their own internal trap.

From the trap the drain flows to the main stack, a vertical pipe leading to the main branch of the sewer line connected to the house. At the point where the soil stack connects with the main drain is a branch fitted with a screw-in plug that can be opened, to allow access in the event of a blockage in the main drain.

The main stack itself continues up through the roof of the building to provide the vent for the system. This vent allows noxious sewer gases to escape into the atmosphere, and the free movement of air throughout the drainage system. Each branch of the drainage system must be connected to the main vent stack or have a separate vent to allow air to escape.

If air is trapped in the drainage system a gurgling sound occurs as the water drains away. Trapped air can also cause water to be siphoned out of the traps, allowing sewer gas to seep into the house through the water seal.