Quick Answer:

A bad smell near an overflow opening usually means debris, soap scum, or standing water has collected in the overflow channel and begun to degrade. Start by flushing the channel and checking what returns. If simple flushing and light cleaning don’t help, follow the step-by-step checks below or call a plumber for a closer inspection.

Why This Happens

• Overflow channels are narrow, out-of-sight passages that connect the tub or sink rim to the drain. They trap hair, soap residue, and mineral buildup.
• Standing water or organic matter in that channel can start to smell as it breaks down or grows bacteria.
• Occasional backflow from a clogged drain can push smelly water into the overflow channel — see Water backing out of overflow slot if you notice water coming the wrong way.

Step-by-Step What to Do

1. Identify the exact source

Confirm the odor is coming from the overflow opening itself, not from the nearby drain, vanity cabinet, or a vent. Put your nose close to the overflow opening and check around the rim and nearby seams for moisture or residue.

2. Simple flush (first and easiest check)

Flush the overflow channel by pouring warm water into the overflow opening and checking what comes back out. Use a cup or a small pitcher and pour slowly so you can see or feel any dirty water returning. Catch the outflow with a towel or bowl so you can inspect it.

3. Repeat with mild cleaner

If the flush returns dirty water or a bad smell persists, repeat the flush using warm water mixed with a little dish soap or a 1:1 solution of warm water and white vinegar. Pour into the overflow opening, let sit a few minutes, then flush again with plain warm water.

4. Remove and inspect the cover (if comfortable)

Many overflow covers are held by a single screw behind a decorative cap. If you can safely remove the cover, look inside with a flashlight. Remove visible hair or gunk with disposable gloves and a paper towel or a soft grabber tool. Don’t force anything metal into the channel.

5. Use a gentle mechanical flush if needed

If residue is stubborn, try a turkey baster or a bulb syringe to force water in and out of the channel, or a flexible bottle brush designed for narrow passages. Avoid using rigid or sharp tools that could scratch or damage the interior.

6. Dry and monitor

After cleaning, dry the overflow area with a towel and run the warm-water flush again. Monitor the smell over the next day; if it returns, the buildup may be further down or there may be a drain issue.

What Not to Do

• Do not pour bleach into the overflow hole as a first step; it can damage finishes and doesn’t remove buildup.
• Do not insert sharp wires or rigid tools into the channel — they can scratch metal or plastic, causing corrosion or leaks.
• Do not mix household chemicals. For example, do not use bleach after vinegar or ammonia-based cleaners; mixing can create harmful fumes.

When to Call a Professional

• Smell persists after multiple flushes and a basic cleaning.
• Visible foul-smelling water keeps coming back or you see continuous discharge — especially if you notice Overflow hole dripping constantly.
• There’s mold growth you cannot remove, or you can’t access the channel without breaking fixtures.
• There are signs of a deeper drain clog, recurring backflow, or water damage in walls or cabinetry.

Safety Notes

• Wear gloves and eye protection when cleaning. Dispose of tissue or towels used to remove gunk.
• Use good ventilation if you use any cleaner indoors. Avoid mixing chemicals.
• Be gentle with fixtures — overtightening screws or prying covers can crack porcelain or plastic.
• If you’re unsure how to remove an overflow cover or suspect a leak behind the wall, stop and call a pro. Repairs behind the wall can require cutting and proper sealing.

Common Homeowner Questions

• Why is the smell worse after using the tub? Short answer: Warm water loosens trapped gunk, releasing odors when it flows into the overflow channel.
• Will the smell go away on its own? Not usually; trapped debris needs to be flushed or removed to eliminate the source.
• Can I use a drain cleaner in the overflow? No—most chemical drain cleaners aren’t designed for overflow channels and can harm finishes or react unpredictably. Use a mild soap or vinegar flush first, or call a plumber.