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Bathtub Drain Smells? The Overflow Plate Is Often the Culprit

Gunk behind the overflow plate and a dry trap cause most tub smells. Clean the overflow with a long brush, then rinse so the trap stays full.

By Jamilur Rahman Updated November 5, 2026 · 7 min read

Time
30 min
Cost
Under $20
Difficulty
Easy
A white bathtub overflow plate removed and resting on a towel beside the open overflow hole on the tub wall
In this guide
  1. Quick answer
  2. Free vs. permanent fix
  3. What you'll need
  4. Why it happens
  5. Try this first (free)
  6. When free fixes aren't enough
  7. Buy the fix
  8. Where the smell lives: the overflow channel
  9. Match the smell to the cause
  10. What to skip
  11. FAQ
  12. Related problems

Quick answer

Why does my bathtub drain smell? Usually it is a slimy buildup of hair, soap and bacteria in the drain and behind the overflow plate, or a dry trap letting sewer gas up. Unscrew the overflow plate, scrub the opening and the drain, then flush with baking soda and vinegar. A long, flexible tub brush reaches the parts a finger cannot, so the smell does not come back.

Free fix vs. permanent fix

Free fix · 30 minutes

Baking soda, vinegar and hot water

  • Unscrew the overflow plate and pull out the gunk
  • Pour baking soda, then vinegar, into the drain and overflow
  • Leave it 15 to 30 minutes, then rinse with hot tap water
  • Run water to refill the trap

How long it lasts: Weeks to months. The slime rebuilds if you never reach the overflow channel.

Most readers choose Permanent fix
Long flexible tub overflow and drain cleaning brush (illustration)
Illustration

A long flexible tub overflow and drain brush

The smell lives in the overflow channel and the first stretch of drain, where water rarely washes. A long, bendable brush scrubs those walls directly, so you remove the source instead of masking it each time.

What to get: Long flexible tub overflow and drain cleaning brush

How long it lasts: Years of upkeep. A monthly pass with the brush stops slime from ever building up.

Check price on Amazon

As an Amazon Associate I earn from qualifying purchases.

What you'll need

  • Screwdriver

    For the overflow plate screws

    You have it

  • Rubber gloves

    For pulling out hair and slime

    You have it

  • Baking soda and white vinegar

    The fizzing flush

    You have it

  • Flashlight

    To see inside the overflow

    You have it
  • Our pick
    Long flexible tub overflow and drain brush (illustration)
    Illustration

    Long flexible tub overflow and drain brush

    Reaches the slime a finger cannot

    Check price
  • Enzyme drain cleaner (illustration)
    Illustration

    Enzyme drain cleaner

    For slime past the brush's reach

    Check price

Why it happens

1

Slime behind the overflow plate

Hair and soap collect in the overflow channel. Water only passes through it when the tub is full, so it never gets rinsed and bacteria grow.

2

Biofilm in the drain

A gray slime coats the pipe wall. Bacteria in it give off a rotten-egg or musty smell that rises when you drain the tub.

3

A dry trap

A tub that is rarely used loses the water in its trap to evaporation. With no water seal, sewer gas comes straight up the drain.

4

Soap scum and hard-water film

Soap and minerals build up around the drain and the overflow and hold damp, which gives a musty or mildew smell.

5

A damaged seal or a vent problem

A cracked pipe, a failed seal or a blocked vent sends smell up through several drains, not just the tub.

Try this first (free)

Do these in order, starting with the simplest.

  1. Unscrew the overflow plate

    Tool used: Screwdriver

    Remove the one or two screws on the plate on the tub wall above the drain. Some plates have a lever linkage attached. Pull it out slowly and set it on a towel.

  2. Look inside and clear it by hand

    Tool used: Flashlight

    Shine a flashlight into the overflow opening. With gloves on, pull out hair and slime that you can reach.

  3. Scrub the overflow channel and drain

    Tool used: Long flexible tub overflow and drain brush

    Work a long flexible brush down the overflow opening and into the drain, then back and forth. Scrub the walls on all sides until the bristles come out clean.

    Long flexible tub overflow and drain brush (illustration)
    Illustration

    Tool for this step

    Long flexible tub overflow and drain brush · Reaches the slime a finger cannot

    Check price on Amazon

  4. Flush with baking soda and vinegar

    Tool used: Baking soda and white vinegar

    Pour half a cup of baking soda down the overflow and the drain, then a cup of white vinegar. Cover and leave 15 to 30 minutes. Skip this if you recently used a chemical cleaner.

  5. Rinse and refill the trap

    Rinse with a pitcher of hot tap water down the overflow, then run the tub tap for a minute. Wash the plate with dish soap before screwing it back.

  6. Treat leftover slime overnight

    Tool used: Enzyme drain cleaner

    If a faint smell remains, use an enzyme drain cleaner as the label says and leave it overnight. It digests slime slowly and does not open a solid clog.

    Enzyme drain cleaner (illustration)
    Illustration

    Tool for this step

    Enzyme drain cleaner · For slime past the brush's reach

    Check price on Amazon

When free fixes aren't enough

If the smell returns within a few days, the slime is deeper than the brush reaches or is growing back fast, and an enzyme cleaner helps. If other drains smell too, you hear gurgling or water backs up, see a plumber. A strong sewage or rotten-egg smell with headaches or nausea means open windows and leave the room. A smell only with hot water points to the water heater, not the tub.

Buy the fix

Still stuck after the free fixes? These are the products we would look at.

Our picks compared
PickProductFixesWho it's forBuy
Best pick
Long flexible tub overflow and drain cleaning brush (illustration)
Illustration
Long flexible tub overflow and drain cleaning brush
slime and hair inside the overflow channel and drain that cause the smell Anyone whose tub smells even after cleaning the surface. Check price
Upgrade pick
Enzyme drain cleaner for odors (illustration)
Illustration
Enzyme drain cleaner for odors
slime inside the pipe beyond the brush's reach Drains with a lingering odor after brushing. Check price
Best pick
Long flexible tub overflow and drain cleaning brush (illustration)
Illustration

Long flexible tub overflow and drain cleaning brush

Fixes: slime and hair inside the overflow channel and drain that cause the smell

Look for: A long, bendable shaft that curves through the overflow opening; Bristles all around the head so it scrubs the pipe walls; Plastic or coated wire that will not scratch the tub finish.

Who it's for
Anyone whose tub smells even after cleaning the surface.
Honest downside
The overflow plate will not come off, or the smell comes from a failed seal or the main line. A brush will not help there.
Check price on Amazon
Upgrade pick
Enzyme drain cleaner for odors (illustration)
Illustration

Enzyme drain cleaner for odors

Fixes: slime inside the pipe beyond the brush's reach

Look for: An enzyme or bacteria-based formula that digests organic buildup; Safe for your pipes and for septic systems if you have one; Directions for an overnight treatment.

Who it's for
Drains with a lingering odor after brushing.
Honest downside
You need a clog opened fast. Enzyme cleaners work slowly, over hours, and do not clear a solid blockage.
Check price on Amazon

As an Amazon Associate I earn from qualifying purchases. We don't show prices because they change, so use the button to see today's price.

How we picked: How we picked: this page is based on plumbing guides on drain traps and tub overflows, public advice on gas smells, and the fixes people report in reviews of tub brushes. We do not test products by hand.

Where the smell lives: the overflow channel

The overflow is a pipe behind the plate on the tub wall. It joins the drain below the stopper. Water only flows through it when the tub is very full, so hair and soap sit there and rot. That is why the smell comes back after a drain clean that skipped it.

Match the smell to the cause

  • Rotten eggs: drain slime, or the water heater if only hot water smells.
  • Musty: mildew in the overflow, caulk or mat.
  • Sewage: a dry trap or vent problem.
  • Strong in every room: call a plumber.

What to skip

Bleach and harsh cleaner poured into the overflow

Strong chemicals rinse straight past the slime on the overflow wall and can harm old pipes. Bleach mixed with vinegar or other cleaners releases toxic fumes, so use one product at a time.

Frequently asked questions

Why does my bathtub smell like sewage or sewer?
A dry trap in a tub you rarely use is the usual cause. Run water for a minute to refill it. If the smell returns, the vent or a pipe may be at fault, so see the related sewer page.
Why does my bathtub smell like rotten eggs or sulfur?
Bacteria in drain slime give off a sulfur smell. If it only appears with hot water, the water heater is the likelier cause. If you cannot place a rotten-egg smell, treat it as a possible gas leak and call your gas company from outside.
Why does my bathtub smell musty or like mildew?
Mildew in the overflow, on the caulk line or on a bath mat that stays damp. Clean the overflow, wipe the caulk and lift the mat so everything dries between baths.
Why does my bathtub smell like pee?
An ammonia-like smell usually comes from bacteria in the drain or overflow, not from the tub itself. If it stays after a deep clean, a failing seal could be leaking sewage, so call a plumber.
Why does my bath smell, and how often should I clean the overflow?
Once a month is enough for most homes, more often with long hair or heavy use. A quick scrub and a hot water rinse stop slime before it makes a smell.

As an Amazon Associate I earn from qualifying purchases. Affiliate disclosure

Long flexible tub overflow and drain cleaning brush (illustration)
Illustration

Our pick: Long flexible tub overflow and drain cleaning brush

Check price