What is the purpose of a trap in a plumbing system?

A trap in a plumbing system primarily serves the purpose of preventing unpleasant odors from entering the living spaces through the drainage system. This is achieved by creating a water seal that acts as a barrier between the sewer gases and the interior of a building. When water fills the lower part of the trap, it blocks the pathway for these gases, thus ensuring that any foul smells from the waste system remain contained.

This water seal is crucial not only for comfort and hygiene but also for health reasons, as sewer gases can contain harmful components. By maintaining an effective water seal, traps play an essential role in the overall functioning of plumbing systems, allowing for safe and sanitary conditions in homes and buildings.

While traps do also collect some small debris and serve other functions in the plumbing system, their primary and most critical role is to prevent the escape of sewer gas odors into the living space. This is why the correct answer focuses on the prevention of unpleasant odors.