• Bathroom Sink Has Black Slime

    Bathroom Sink Has Black Slime

    Quick Answer:

    Dark, slimy buildup around the drain is usually bacterial or mold biofilm mixed with soap scum, hair, and mineral deposits. Clean it by removing the stopper, scrubbing the visible film, and flushing the overflow and drain passages. If the slime returns immediately or you have strong sewer odors, call a plumber.

    Why This Happens

    • Warm, damp environments around the drain let bacteria and mold form a slippery biofilm.
    • Soap, hair, skin oils and toothpaste feed the film and help it stick to metal and porcelain.
    • Slow drainage or a partially clogged trap holds moisture and organic matter, letting the slime build faster.
    • Overflow channels are often forgotten and provide an out-of-sight place for growth.

    Step-by-Step What to Do

    1. Prepare

    • Put on gloves and eye protection. Open a window or run a fan for ventilation if you plan to use cleaning products.
    • Have a small bowl, old toothbrush or a narrow pipe brush, a rag, a flathead screwdriver or pliers (if needed), and a bucket ready.

    2. Remove the stopper

    • Many stoppers pull straight up or are released by a pivot rod under the sink. Place a towel in the sink and a bucket under the P-trap to catch drips.
    • Set the stopper aside and inspect it — slime often accumulates on the shaft and underside.

    3. Scrub the biofilm

    • Use the toothbrush or pipe brush with warm soapy water to scrub all visible slime from the stopper, drain opening, and visible parts of the tailpiece.
    • For stubborn buildup, a diluted bleach solution (about 1:10 bleach to water) or an enzyme cleaner can be used carefully. Rinse thoroughly afterward. Avoid abrasive pads that will damage finishes.

    4. Flush the overflow

    • Pour warm soapy water into the overflow hole to dislodge grime. If your overflow has a removable cover, remove it and clean behind it.
    • You can use a small bottle brush or a pipe cleaner to reach deeper into the overflow channel, then flush with clean water.

    5. Clear and flush the trap

    • If drainage is slow, loosen the P-trap and clean out trapped hair and gunk. Rinse the trap and run hot tap water to flush the line.
    • Reassemble the trap, reinstall the stopper, and run the faucet for a minute to check for leaks and carry remaining debris down the drain.

    6. Finish and prevent return

    • Wipe all surfaces dry. Consider a weekly quick scrub or an enzyme drain cleaner used per product directions to reduce regrowth.
    • Trim hair, avoid rinsing greasy substances, and run water for 30–60 seconds after use to keep the trap and overflow flushed.

    What Not to Do

    • Do not mix cleaners — never combine bleach with ammonia or vinegar; mixing chemicals can create dangerous gases.
    • Do not pour concentrated acids or industrial drain cleaners down a bathroom sink; they can damage pipes and finishes and are hazardous to handle.
    • Do not use a metal coat hanger or sharp objects to poke the drain; you can damage the plumbing or push clogs further in.

    When to Call a Professional

    • Persistent or recurring slime that returns within days despite cleaning.
    • Strong sewer or rotten-egg odors that don’t improve after cleaning the drain and overflow.
    • Repeated slow drainage, backups, or leaks under the sink when you clean the trap.
    • If you suspect mold spreading beyond the sink area or if you have health concerns from the growth.

    Safety Notes

    • Wear gloves and eyewear when handling cleaners or scrubbing biofilm. Keep children and pets away during cleaning.
    • Use cleaner dilution instructions on the label. Work in a well-ventilated area and rinse thoroughly after using any disinfectant.
    • Test a small hidden area first if using bleach near colored finishes. Never mix different chemical cleaners.

    Common Homeowner Questions

    • Why does it smell worse after I clean? — Disturbing built-up biofilm can release trapped gases; rinse and ventilate after cleaning. See Bathroom Sink Smells Like Sewer Gas After Sitting for more on persistent odors.
    • Will pouring boiling water help? — A short pour of very hot water can help loosen grease but may damage some fixtures or seals; use caution and check manufacturer guidance.
    • My sink only clogs with hot water — what then? — That pattern suggests grease or a condition affected by temperature; consider professional inspection and see Bathroom Sink Drains Slow Only With Hot Water.