If your bathroom sink smells bad even after you scrub the basin, the overflow opening may be the hidden source.
This guide explains how to clean smell from bathroom sink overflow and stop the odor from coming back.
Why the Overflow Hole Smells
The overflow opening is the small slot or hole near the top of many bathroom sinks that helps prevent flooding.
It can trap soap residue, toothpaste, skin oils, mildew, and stagnant water, creating an odor even when the visible sink looks clean.
Because the passage is narrow and often stays damp, it can hold organic buildup that standard surface cleaning misses.
In some cases, foul smells can also come from bacteria in the drain trap, but the overflow channel itself is a common odor source.
What You Need Before Cleaning
Gather a few basic supplies before you start.
Most homes already have these items:
- Warm water
- Baking soda
- White vinegar
- Dish soap
- A small funnel or squeeze bottle
- Pipe cleaner, cotton swabs, or a small bottle brush
- Old toothbrush
- Microfiber cloth or paper towels
If you want a stronger approach, you can also use an enzyme cleaner labeled safe for sinks and drains.
Enzyme-based products help break down organic material without the harsh fumes of stronger chemicals.
How to Clean Smell from Bathroom Sink Overflow
1. Flush the overflow channel with warm water
Start with warm water to loosen debris.
Pour it slowly into the overflow opening so it moves through the channel and into the drain.
This initial rinse helps remove loose soap scum and prepares the area for deeper cleaning.
2. Apply a baking soda solution
Mix a few tablespoons of baking soda with warm water to form a thin paste or slurry.
Use a squeeze bottle, syringe, or small funnel to direct the mixture into the overflow opening.
Let it sit for 10 to 15 minutes.
Baking soda helps neutralize odor and can loosen buildup on the inside walls of the passage.
If the smell is mild, this step alone may improve the odor noticeably.
3. Add white vinegar for a fizzing reaction
After the baking soda has had time to sit, pour in a small amount of white vinegar.
The fizzing action can help lift grime from the hidden channel.
Keep the mixture in the overflow for another 10 minutes before flushing with warm water.
Do not use excessive amounts at once.
A controlled amount is more effective and easier to rinse away.
4. Scrub the visible opening
Use an old toothbrush or cotton swabs to clean around the overflow slot on the sink surface.
Wipe away any buildup, toothpaste crust, or mildew around the rim.
This matters because residue at the opening can keep feeding odors inside the passage.
5. Clean the channel mechanically
Insert a pipe cleaner, flexible brush, or narrow bottle brush into the opening as far as it comfortably reaches.
Move it gently back and forth to dislodge trapped sludge.
If you use a brush, rinse it often so you are not spreading grime back into the hole.
For sinks with stubborn buildup, repeat the baking soda and vinegar treatment after brushing.
Alternating chemical loosening with mechanical scrubbing usually works better than either method alone.
6. Rinse thoroughly
Flush the overflow and drain with plenty of warm water.
This removes loosened particles and leftover cleaner.
A poor rinse can leave residue behind, which may contribute to new odors later.
How to Treat Stubborn Odors
If the smell remains after a basic cleaning, the problem may be deeper in the overflow path or connected drain.
Try these targeted fixes:
- Use an enzyme drain cleaner: Follow the product directions and allow enough dwell time for organic buildup to break down.
- Check the sink drain trap: A dry P-trap can allow sewer gas to enter the room.
Run water if the sink has not been used recently.
- Inspect for mold growth: Persistent dampness around the overflow or faucet base can support mildew and bacteria.
- Clean with diluted dish soap: If grease or product residue is the issue, a few drops of dish soap in warm water can help break it up before rinsing.
If you smell rotten eggs or sewage after cleaning, the odor may come from plumbing vents, the P-trap, or a drain issue rather than the overflow alone.
In that case, the sink may need a plumbing inspection.
What Not to Use
Avoid mixing cleaning chemicals.
In particular, do not combine vinegar with bleach or use multiple drain cleaners at the same time.
These combinations can create dangerous fumes or reduce cleaning effectiveness.
Avoid very harsh tools that can scratch porcelain, acrylic, or metal finishes.
A narrow brush should be flexible enough to clean the passage without damaging the sink.
How to Prevent Overflow Smells
Once the odor is gone, a few simple habits can keep it from returning:
- Rinse the sink overflow with warm water once a week.
- Scrub the overflow opening during routine bathroom cleaning.
- Keep the sink dry after heavy use when possible.
- Avoid letting toothpaste and shaving cream buildup sit near the opening.
- Run hot water periodically if the bathroom sink is rarely used.
If your household uses hair products, mouthwash, or heavy cosmetics near the sink, clean more often.
These products can leave residue that feeds odor-causing buildup inside the overflow channel.
When a Professional Should Inspect the Sink
Call a plumber if the smell returns quickly after cleaning, if water drains slowly, or if you notice gurgling sounds from the sink.
Recurring odor can point to a partial clog, ventilation problem, or bacteria buildup in a deeper part of the plumbing system.
A professional can test the drain, inspect the P-trap, and confirm whether the overflow channel is actually the source.
That is especially useful if the bathroom smells unpleasant but the sink surface and overflow opening appear clean.
Quick Routine for Ongoing Odor Control
- Weekly: Flush the overflow with warm water.
- Monthly: Clean the opening with baking soda and vinegar.
- As needed: Brush the visible slot and surrounding rim.
- Seasonally: Check for leaks, mildew, or dry traps.
With this routine, you can keep the overflow channel cleaner, reduce bacterial growth, and prevent stale sink odors from building up again.