Drain flies live where you'd least expect to find a winged creature—within the depths of your sticky, gunky drains. The reason you'll find drain flies inside your sink or shower drains is because they feed on and lay eggs in the decomposing gunk that lines slow or clogged drains. If you spot drain flies buzzing around your sink, here's how to remedy the situation. First, determine which drain they’re flying out of. Chances are there's a clog in that drain. You'll need to clear it before you can lose the bugs. Use a pipe snake or pipe brush to scrub away the built-up slime, then open the P-trap underneath the sink to remove any remnants of the clog. Close the system again, and finish by pouring an enzyme cleaner down the drain to remove the rest of the residue and any lingering drain fly eggs.