What is the function of a plumbing trap under sinks?

The function of a plumbing trap under sinks is to retain water, which effectively blocks sewer gases from entering the home. When water is held in the trap, it creates a seal that prevents these harmful gases from escaping into the living spaces. This is vital for maintaining indoor air quality and preventing unpleasant odors associated with sewer gases.

The design of traps, often in a U or S shape, ensures that a small quantity of water remains in the bend even after the sink is drained. This unbroken water barrier is crucial; if the trap were to dry out, it would no longer serve its purpose, and fumes could potentially infiltrate the home.

In the context of the other choices, improving drainage speed is not a function of the trap, as it is primarily designed for blocking gases, not enhancing flow. Allowing sewer gases to escape is counterproductive to its primary role. While collecting sediment from wastewater has other applications in plumbing systems, it does not pertain specifically to the function of the trap under sinks. Therefore, retaining water to block sewer gases is the most accurate description of the trap’s function.