Where bathroom drain smells come from
Every drain has a trap, a U-shaped bend that holds a little water to block sewer gas from coming back into the room. When a sink, shower or floor drain goes unused for a couple of weeks, that water evaporates, especially in Denver's dry air with the heat running. The trap dries out, and sewer gas comes straight up the drain.
Other common sources are the overflow opening on a bathroom sink, which collects soap scum and hair that turn sour; a buildup of hair and residue just below the drain stopper; a toilet with a failing wax ring at the base; and a plumbing vent that is blocked, which can make traps gurgle and lose their water. In older Highland and LoHi homes that have been remodeled, a drain added in a basement or a new bathroom sometimes was not vented properly.
Clue and likely cause
| What you notice | Likely cause | Who fixes it |
|---|---|---|
| Smell after the unit sat empty, gone after running water | Dry trap | Cleaner: run water in every drain at each turnover |
| Smell at the sink, worse near the overflow hole | Dirty overflow channel | Cleaner: flush and brush the overflow |
| Smell around the base of the toilet, stain or rocking | Failed wax ring or loose toilet | Plumber |
| Gurgling drains and traps that keep emptying | Blocked or missing vent | Plumber |
| Smell in a basement bathroom or floor drain | Dry floor drain or sewer line problem | Cleaner first; plumber if it persists |
A turnover routine for drains
- Run every fixture.Run each sink, shower and tub for about thirty seconds and flush every toilet, including in rooms guests did not use. Pour a quart of water into floor drains.
- Clean the stoppers and overflows.Pull and clean pop-up stoppers and shower strainers, and flush the sink overflow with hot water and a small brush.
- Check the toilet bases.Look for water, staining or movement at the base of each toilet. A toilet that rocks needs attention.
- Write it down.Note any drain that smelled before running water. A drain that keeps drying out may need a trap primer or a plumber's look at the vent.
Common questions
How long does it take a trap to dry out?
It depends on the trap and the air, but in dry, heated Denver homes, a rarely used drain can lose its water seal in a few weeks.
General information for LoHi, not a quote or professional advice. In an emergency, call 911.