Drain flies breed in heavily decaying organic matter that remains fairly wet. They are commonly found in sewage treatment facilities. In other commercial buildings they are often seen in restrooms, mop closets and boiler rooms, breeding in drain traps, sump pumps, and any very wet, poorly maintained area. Drain flies are weak fliers, and indoors are usually seen crawling on walls or other surfaces. When they do fly, it is usually only for a few feet and then in characteristic short, jerky lines.

Heavily decaying organic matter such as is found in sewage sludge is their preferred diet.

Finding the breeding sites and removing them is key to controlling drain flies. Inspection needs to focus on any place where wet organic matter has accumulated, including slimy drains, dirty garbage cans, bird baths or feeders, clogged roof gutters, moist compost and septic tanks. Clean drains regularly using appropriate drain cleaners or bacterial drain cleaning products.