What is the essential function of a trap in plumbing?

The essential function of a trap in plumbing is to prevent odors from entering a building's interior. Traps are designed to hold a small amount of water, creating a barrier between the sewer gases and the indoor environment. This water seal effectively blocks unpleasant smells and harmful gases that can arise from the sewage system, ensuring a healthier and more comfortable living space.

While traps are involved in the overall functioning of plumbing systems, their primary purpose centers around maintaining air quality by preventing odors. Other features, such as allowing water flow or facilitating drainage, are secondary functions supported by the design of the trap, but they do not encompass the trap's main role. Additionally, managing pressure is not a function of traps but pertains more to specific designs and components in a plumbing system, such as vents.