Symptoms
- Musty or mildew-like smell near the laundry room drain
- Smell noticeable especially after the washing machine has been idle
- No visible water backup
- Smell may worsen in humid weather
Likely causes
- CommonTrap partially or fully dried outFloor drains not used directly (only receiving occasional washer overflow) can dry between uses.
- CommonLint and detergent residue built up around the drain grateLint from the washer's air or overflow can settle and hold moisture, encouraging mildew smell.
- PossibleStanding moisture in the surrounding floor areaA generally damp laundry room can contribute to a musty smell beyond just the drain.
- PossibleMold growth just inside the drain openingDark, damp conditions inside the drain can support mold growth.
What to do
- Pour a bucket of water down the floor drain to refill the trap if it has been sitting dry.
- Remove the grate and scrub around the opening with a brush and a mix of baking soda and vinegar.
- Check the surrounding floor for any general dampness or poor ventilation contributing to a musty smell in the room overall.
- Run a dehumidifier or improve ventilation in the laundry area if it tends to stay humid.
- Repeat the water-refill routine every few weeks if the drain isn't used directly and tends to dry out.
- If the smell persists despite cleaning and refilling, consider a trap seal product designed for infrequently used floor drains.
Tools and parts
- Bucket
- Brush
- Baking soda
- Vinegar
Floor drain trap sealSearch: “floor drain trap seal insert”
When to call a pro
Call a plumber if the smell continues despite regular cleaning and refilling, since it could point to a drain or venting issue.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.