Drain Flies and Bleach
Drain flies can be very difficult to control. The eggs are laid in the gelatinous mass which lines drain pipes, and larvae hatch and feed on the plant and animal forms found in the mass. Adult drain flies appear seemingly one at a time and the homeowner can become frustrated.
Some homeowners have tried to pour bleach down drains to control drain flies. While bleach might control some larvae, bleach passes quickly down the drain and does not penetrate the sometimes thick buildup. In addition, bleach might not be suitable for older pipes as full-strength bleach from the container is corrosive. Also, some homeowners have tried bleach followed by ammonia for good measure. This is extremely dangerous, as mixing bleach and ammonia creates chlorine gas, a dangerous and potentially fatal gas if inhaled.
The most modern control is to remove the film through the use of enzymes. Foaming enzymes applied by professional pest control companies will break down the film through the action of the enzymes. Enzyme treatment will not form any dangerous byproducts nor should it harm pipes.