The book In the Kitchen by J.C. Greenburg, tells the story of Alexander, his cousin Judy, and Thudd the robot, who get shrunken and encounter many different insects on their journey back to their original size, including drain flies.

Drain flies, also known as moth flies, live in areas like sink drains, sewage facilities, storm drains, dung, and rotten materials. In their larval stage they provide the valuable service of breaking down wastes. But most humans see them as annoying pests because they can become numerous around bathroom or kitchen sinks. Amazingly, drain flies breed in drains, even though there is a constant flow of hot, soapy, dirty water, running over them.

Information from:
http://www.uky.edu/agriculture/entomology/entfacts/struct/
ef615.htm