Why the Floor Drain Smells

The smell is low, near the floor, and it is more rotten than dusty. Floor drains are there so a leak or a wash-down has somewhere to go. They also hold a little water in the trap, the bent section of pipe, so sewer air stays in the pipe. When that water evaporates, the drain smells. Basements, laundry rooms, garages, and mechanical rooms do this when nobody uses the drain for weeks.

Pour water. A pitcher, slowly, into the floor drain. If there is a cover, you may need to lift it. You are refilling the trap, not flooding the floor. If the rotten smell fades after the water sits, the trap was dry. That is a common, unglamorous win. Pour again every few weeks if the drain rarely sees water, or ask a plumber about a trap primer if this is constant and you are tired of the pitcher. The pitcher is a fair test and a fair habit for a rarely used drain.

If the smell does not fade, or it returns the same day with the trap full, stop pouring chemicals after it. A missing trap, a cracked trap, a dried-out trap that is not actually connected the way you think, or a vent problem needs a plumber. Baking soda and a random bottle will not rebuild a trap. Mixed cleaners are a bad idea in a floor drain you are kneeling over.

Musty and rotten are worth separating. Musty can be a wet basement around the drain, cardboard on the slab, a dehumidifier that quit. Rotten and sewer-like, right at the drain, is the trap and the sewer side. If both are present, refill the trap and also look at the room's moisture. One scent can hide the other until you do.

The cover can be slimy. Lift, rinse, and dry the cover if it comes up easily. Do not pry a drain out of the concrete as a curiosity. If sewage is backing up, not just smelling, that is a plumber now, not a pitcher experiment. Standing sewage is a health mess. Keep kids and pets away and call.

Floor drains in mechanical rooms can sit next to a furnace. Do not confuse a sewer smell with a gas smell. Gas means leave and call the gas utility from outside. Sewer means the drain. Your nose usually knows, and if you are unsure, treat it as gas and get out.

Write whether water fixed it, and how fast it returned. A plumber can use that. "We poured water and it was fine for a month" is a primer conversation. "We poured water and it never changed" is a different visit.

Mark the calendar when you pour, so the next smell has a date. If it returns in two days, you are not dealing with ordinary evaporation. If it returns in six weeks, a reminder to pour is the whole maintenance plan. Those two timelines should not get the same repair.

While you are on the floor, look at the concrete around the drain. A wet ring and a musty smell are moisture. A dry floor and a rotten whiff are the trap. Saying both words to a plumber is fine if you truly have both. Saying only that the basement smells gets you a guess.

Do not tape the cover shut to hide the odor. You may also hide a backup until it finds another exit. Water in the trap, or a plumber if water does not work, keeps the drain a drain. A sealed cover is how a small smell becomes a surprise in the next fixture.

Stuffy mornings that worry you belong with a doctor. Anything that means cutting drywall or working on gas equipment belongs with a licensed pro.

Floor drains are a simple picture in When Your House Doesn't Feel Right. ClearNest, $2.99, at https://clearnestair.com/book.