Small flies keep appearing near a drain

Symptoms

• Small, fuzzy dark flies near a sink or floor drain
• Flies seem to appear from nowhere, especially at night
• No obvious food source nearby attracting them
• Problem persists over days or weeks if untreated

Likely causes

• CommonDrain flies breeding in organic buildup inside the pipeThese flies lay eggs in the slimy film of soap scum, hair, and food residue that lines drains.
• CommonSlow-draining or rarely used drain allowing more buildupStagnant conditions are ideal for the organic film these flies need.
• PossibleSimilar buildup in a floor drain or overflow rather than the main drainSometimes the source is a less obvious nearby drain.
• PossibleFruit flies from a food source rather than drain fliesWorth distinguishing, since the fix is different if it's actually a food-source fly.

What to do

1. Confirm the flies are coming from the drain by placing clear tape sticky-side down over the drain opening overnight and checking for trapped flies in the morning.
2. Clean the drain thoroughly with a bottle brush to physically remove the organic film, since gel cleaners alone often don't reach it.
3. Follow with a baking soda and vinegar treatment, letting it sit 15–30 minutes before flushing with hot water.
4. Repeat the cleaning every few days for a week or two, since it takes multiple treatments to fully break the breeding cycle.
5. Check nearby drains (overflow, floor drain) for the same buildup, since flies can be coming from a different drain than expected.
6. If flies persist despite thorough cleaning, an enzymatic drain cleaner designed for organic buildup can help finish the job.

Tools and parts

• Bottle brush
• Baking soda
• Vinegar
• Tape (for testing)

When to call a pro

Call a plumber if flies persist after several thorough cleanings, since there may be a hidden source like a cracked pipe or hidden standing water.

Safety