Pour boiling water down the drain daily for several days
Scrub the drain opening and inside the drain with a stiff brush
Clean the drain trap and remove any sludge or buildup
Use a drain gel cleaner to break down organic residue
Flush the drain with baking soda followed by vinegar, then hot water
Remove and clean the sink stopper or drain cover
Check and clean nearby garbage disposals
Wipe up spills and keep the sink dry when not in use
Take out trash and compost regularly
Store fruit in the refrigerator or sealed containers
Fix leaks and eliminate standing water
Set a vinegar trap near the drain
Repeat cleaning until flies are gone
Call a plumber if the infestation persists