Quick Answer:
Changing dish soap or dishwasher detergent can leave a different film in the sink and trap that bacteria and mold feed on. Rinse the sink well to remove detergent film, switch back to a simpler soap for about a week, scrub the baffle and drain opening where the slime forms, and then run plenty of water so residue doesn’t sit in the trap area.
Why This Happens
Some detergents leave more residue or change the balance of surfactants in the sink. That residue plus food particles and damp conditions lets a thin bio-film develop quickly. The slime often starts right at the drain opening, around the strainer or baffle, and inside the top of the trap where water sits. If the smell seems tied to parts you can see above the sink, check the overflow—see Odor from overflow hole. If you recently used a dishwasher and the scent seems tied to that cycle, look into the connection to the drain: Smell after dishwasher drain.
Step-by-Step What to Do
Step 1 — Rinse the sink thoroughly
Start by flushing the entire sink with hot water for a few minutes. The goal is to wash away any fingerprint-thin detergent film so it doesn’t keep feeding slime during cleaning.
Step 2 — Switch back to a simpler soap for a week
Use a basic, unscented dish soap or a plain liquid castile soap for several days. This removes the variable of a new formulation while you treat the slime. If the smell improves, the residue from the previous product was likely the trigger.
Step 3 — Scrub the baffle and drain opening where slime forms
Remove the sink strainer or baffle if possible and scrub all visible surfaces with a stiff brush or an old toothbrush. Focus on the underside of the baffle, the upper drain opening, and the crevices where slime hides. Use a mild scrub solution (hot water with a little dish soap, or a 1:1 mix of white vinegar and water) and mechanical action to remove the bio-film.
- Tools: gloves, stiff brush/toothbrush, bucket, sponge, possibly a small mirror for tight spots.
- For stubborn spots, an enzyme sink cleaner can help break down organic buildup without harsh fumes.
Step 4 — Run plenty of water afterward so residue doesn’t sit in the trap area
After scrubbing, flush the drain with hot water for several minutes so loosened residue is carried through the trap. If you have a garbage disposal, run cold water while the disposal runs briefly to clear its chamber. Keeping the trap flushed prevents material from settling and re-forming slime.
What Not to Do
- Don’t assume the detergent is “bad” and ignore the slime—bio-film needs mechanical cleaning to remove it.
- Don’t rely only on pouring chemical cleaners without scrubbing; those products may reduce odor temporarily but won’t remove the film unless you physically clean the surfaces.
- Don’t mix cleaning chemicals (for example, bleach and ammonia); that can create dangerous fumes.
- Don’t ignore persistent odors; if odors persist after switching back and cleaning, a plumber can check for a deeper drain issue.
When to Call a Professional
Call a licensed plumber if you have any of the following after trying the steps above:
- Persistent sour or sewage-like odor that won’t go away.
- Repeated slime or recurring clogs despite cleaning.
- Gurgling, slow drains, or signs of a deeper blockage or venting problem.
A plumber can inspect the P-trap, the dishwasher tie-in, the venting and the drain line for hidden buildup or damage and advise safe treatments.
Safety Notes
- Wear gloves and eye protection while scrubbing. Keep the area well ventilated.
- Do not mix cleaning chemicals. Follow label directions for dilution if you use bleach or other cleaners.
- Be cautious when removing strainers or working around a garbage disposal—disconnect power if you must reach into the disposal area.
- If you’re unsure how to access the trap or you encounter sewage odors, stop and call a professional rather than forcing an unfamiliar repair.
Common Homeowner Questions
- Can a new detergent actually feed bacteria? Yes — if it leaves a film or residue that traps food particles, it can speed bio-film growth.
- Will vinegar alone remove the slime? Vinegar helps but mechanical scrubbing is usually needed to remove the bio-film completely.
- Is it safe to pour bleach down the drain? Occasional diluted bleach rinses can be used cautiously, but don’t mix with other cleaners and don’t rely on bleach instead of scrubbing.
For more related articles, see the Food Waste Odors & Bio-Buildup hub.