Pour boiling water down the drain daily for several days
Scrub the inside of drains, pipes, and overflow openings with a stiff brush
Use an enzyme-based drain cleaner to remove organic buildup
Clean sink stoppers, strainers, and drain covers thoroughly
Remove and clean P-traps if accessible
Fix leaks and eliminate standing water
Keep drains dry when not in use
Dispose of garbage, food scraps, and compost promptly
Clean trash cans and recycling bins regularly
Check and clean nearby floor drains, shower drains, and utility sinks
Use sticky traps near affected drains to catch adults
Seal cracks and gaps around plumbing and walls
Repeat cleaning until flies are gone
Call a plumber or pest professional if the problem persists