Drain & Sewer
P-Trap
A P-trap is the curved pipe fitting found beneath every sink, tub, and shower drain — the U-shaped section visible under most bathroom and kitchen sinks. Its purpose is to hold a small amount of water at all times, creating a liquid seal that prevents sewer gases (hydrogen sulfide, methane, and other odorous or potentially harmful gases) from entering the living space through the drain opening.
The P-trap works by retaining water in its lower curve. As long as water flows through regularly and the trap doesn't dry out, it maintains its seal. Drains that are rarely used — a guest bathroom sink, a floor drain, a utility sink — can have their P-traps evaporate dry, allowing sewer gases to enter. If you smell sewer gas near an infrequently used drain, run water through it to refill the trap before assuming you have a more serious problem.
What This Means for You
If you notice a sewage smell coming from a floor drain or sink drain, try pouring a quart of water into the drain to refill the P-trap before calling for service. A floor drain in a basement or utility room that is rarely used is the most common source of unexplained sewer odors in Minnesota homes. If refilling the trap doesn't resolve the odor, call for inspection.