Gnats are annoying little insects that like warm, moist climates and locations. They are most commonly brought into your home on food items but may find their way in if you are having a very warm and moist summer. Locations such as sink drains, garbage disposals and overflow holes are ideal locations for these pesky little creatures. Eliminating these unwanted house guests is very simple using a common household item -- bleach.
Fill a turkey baster with bleach.
Insert the end of the baster in the overflow hole.
Squeeze the bleach into the hole until the baster is empty.
Plug the hole with a rag for one hour. Close the drain to help keep the fumes within the pipes to kill any gnat-like bugs that may be breeding in that area.