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

The purpose of a trap in a plumbing system is to prevent sewer gas from entering the building. Traps are designed to maintain a small amount of water in a bend, which acts as a barrier against odors and harmful gases that can come from the sewer system. This water seal is crucial for maintaining indoor air quality and ensuring that residents are not exposed to potentially toxic or foul-smelling gases.

While allowing water to flow freely, filtering solid waste, and ensuring proper drainage are important functions of a plumbing system, they are not the primary function of a trap. In fact, traps may slightly restrict the flow of water in order to maintain that necessary water seal, underscoring the priority of protecting indoor air over the unrestricted flow of waste.