Quick Answer:

Black, slimy gunk coming up around a drain is usually a build-up of biofilm—soap scum, body oils and bacteria—not raw sewage. Check for backup signs like rising water, strong sewage odor or gurgling. Remove the stopper, clean the drain walls and overflow, flush the trap, and sanitize. If the slime returns quickly or you see clear backup symptoms, call a plumber.

Why This Happens

• Soap, shampoo, hair and skin oils collect on pipe walls and in the overflow channel. Over time bacteria grow in that film and create dark, slimy deposits.
• Poor flow, slow drainage or infrequent cleaning makes a thicker film, which can flake off or migrate back up the drain opening.
• If the build-up returns rapidly or you have rising water, gurgling, or sewage smells, the issue may be further down the line or a partial clog.

Step-by-Step What to Do

1. Remove the stopper and inspect

• Take out the stopper (or lift the plug) and look down the drain. Use a flashlight to see if the slime is just at the mouth of the drain or deeper.
• Pick out visible hair and debris with a disposable glove or a drain snake designed for hair.

2. Clean the drain walls and overflow

• Use a long, soft bottle brush or an old toothbrush to scrub the drain walls and the overflow slot. A diluted household cleaner or a mixture of warm water and mild detergent works well.
• Rinse as you scrub so loosened slime leaves the pipe rather than sticking to other surfaces.

3. Flush the trap

• Run hot (not boiling) water for several minutes to help dissolve greasy deposits.
• If water flow still seems restricted, remove and clean the P-trap if you are comfortable doing so: place a bucket under the trap, loosen the slip nuts, empty and clean it, then reassemble carefully.

4. Check if the slime returns quickly

• Wait 24–48 hours after cleaning. If the black slime is back within a day or two, note whether there are slow drains, gurgling noises, or odors—these suggest a deeper clog or sewer issue.

5. Sanitize safely

• After removing the slime, wipe surfaces with a diluted bleach solution (follow label directions) or a household disinfectant. Wear gloves and ensure good ventilation.
• Rinse thoroughly after disinfecting so residues don’t damage finishes.

What Not to Do

• Do not mix cleaners. Never combine bleach with ammonia or other cleaners—this can produce dangerous gases.
• Avoid aggressive scraping that can damage porcelain, enamel or metal finishes; use soft brushes and plastic tools instead.
• Don’t assume it’s sewage without checking for backup symptoms like rising water, gurgling or a sewage smell.

When to Call a Professional

• If the slime keeps returning within a day or two despite cleaning.
• If you notice rising water, persistent slow drainage, gurgling noises, or foul sewage odors.
• If you find leaks under the floor or wet spots after using the drain—see Drain Leaks Under the Floor After Use.
• If backups happen only when you use certain fixtures (for example, the shower) — see Drain Backs Up Only When You Shower.

Safety Notes

• Wear gloves and eye protection when cleaning drains and when handling disinfectants.
• Ventilate the room when using chemical cleaners or bleach. Follow label instructions exactly.
• If you remove the P-trap, keep a bucket underneath and reassemble carefully to avoid leaks. If you’re not comfortable, stop and call a plumber.

Common Homeowner Questions

• Is this slime dangerous? Not usually—it’s typically bacterial biofilm and not raw sewage if there are no backup signs.
• Will a paste of baking soda and vinegar solve it? It can help loosen some residue, but it’s not a guaranteed long-term fix and should not replace physical cleaning.
• How often should I clean to prevent it? Monthly quick cleanings of visible drains and overflow areas help prevent heavy build-up.