The quickest way to control a gnat infestation is to use a pesticide aerosol or bug bomb approved for indoor use. Be sure to follow labeled directions for safe use. Cover any exposed fruit or food to prevent. If you must leave dirty dishes in the sink, fill the sink with some soapy water to trap any gnats or flying pests that might seek out the food. Repair or replace damaged weather-stripping, and screening to prevent pest entry