Drain flies are small (1/8 inch long), black, and have a fuzzy appearance. They often fly in swarms and are most easily identified by their small size and their fuzzy appearance.
The best way to get rid of drain flies is to eliminate their food sources by thoroughly cleaning your kitchen and bathroom. You can also use commercial fly traps or bait. If you have a severe infestation, you may need to call a professional exterminator.