What Is a House Trap for the Sewer?


A house trap for the sewer is a small piece of elbow pipe, sometimes called a P-trap, that is designed to hold water and prevent sewer gas from backing up in to the house. Sewer gas can be a health hazard, in addition to carrying an unpleasant odor. House traps are required for most building codes as sewer gas can be high in methane and consequently pose a risk of explosion.

How Traps Work

  • A plumbing trap consists of a small elbow piece of pipe. This pipe is installed in such a way that it remains filled with water even when the drain is not in use. The water acts as a seal for gases that may build up in the sewer or drain line. Occasionally, if a house is unoccupied for a long time, the water in a house trap can evaporate and allow sewer gas to escape. However, this only happens if all drains in the house go unused for a prolonged period of time.

Septic Odor Issues

  • A malfunctioning house trap or a drain lacking a trap can allow sewer gas to permeate through in to the house. This will cause an intense, sour smell reminiscent or rotten eggs or sulfur. Sewer gas is potentially a health hazard and the drain trap should be repaired or replaced as soon as the odor is noted.

Trap Clogs

  • A trap is designed to hold water and seal off sewer gas but, at times, it can hold other things as well. A house trap is a good first place to check when faced with a clogged sewer or drain line. Use a plumber's snake to check for and clear out any clogged debris.

Trap Replacement

  • When replacing a trap, care should be taken to ensure it is installed properly. Additionally, you may want to opt for a double clean out model which has small plugs that can be removed on both sides of the trap. This makes cleaning the trap out significantly easier and can save you a lot of headaches in the future.

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