Why Are Flies Coming Out Of Bathroom Drains?

At Whywait Plumbing we have had a number of calls from clients who are concerned they are about to be overrun by small flies in their bathroom. Generally the concern is that they are in large numbers and no matter what is done to kill them there is always more the next day.


Cleaning Your Drains Doesn’t Get Rid Of Drain Flies!

Many Whywait Plymbing clients had cleaned the bathroom until it could be cleaned no more and so by the process of elimination had decided that they were coming out of one of the drains in the bathroom. But no matter how often some of them sat and observed the drains they never saw any of them emerging from the drain in the shower or basin or the floor waste.

What many people constantly observed was the flies flying or mainly sitting on the walls or ceiling in the bathroom. Whywait Plumbing can confirm that what everyone had was what are commonly known as drain or moth or bathroom flies.


What Do Drain Flies Look Like

what do drain flies look like
A typical looking drain fly on a bathroom wall

Drain flies are dark grey flies and are 2-4mm in length with hairy moth-like wings. They have a jerky flight as they are poor fliers and usually are found close to the drain or area of origin. Hence why they seldom stray outside the bathroom as in most cases they are breeding in the bathroom floor trap. Drain flies do not bite and are not known to transmit disease of any sort nor do they damage clothes or linen and are considered to more of a nuisance value in a home.


The adult flies and larvae can be controlled by eliminating or reducing breeding sites. If the infestation is minor the pouring of bleach into the floor trap will usually work in killing them. However if that does not solve the problem then you will need to kill them by thoroughly cleaning the drain lines and or sealing of the floor trap.


The reason that they continually seem to be in large numbers despite constantly killing them is because eggs hatch in 32 to 48 hours when the temperature is above 20 degrees. The larvae mature in 9 -12 days and feed on the decaying organic matter that accumulates in the floor trap. The life cycle of a fly is 1-3 weeks. Adults live about 2 weeks, with old ones dying and new ones emerging. They feed on the waste water in the floor trap. During the day the adults rest in shaded areas such as under the basin or on walls near plumbing fixtures and on the sides of showers and baths. Most activity occurs during the evening when the flies are seen hovering about.


Septic Tanks Breeders

If you are on acreage and have septic tanks they may breed in large numbers and then may be carried by prevailing wind to nearby homes up to 3 kilometers away. Adult flies are small enough to pass through ordinary window mesh screens.


Thorough Cleaning of Drain and Traps

It is the experience of Whywait Plumbing that cleaning of the drains from the basin, shower and bath that discharge into the floor trap is only part of the answer. It is also beneficial to clean the floor trap thoroughly and pour bleach down the drain although this is washed away with each use of any of the fixtures.


DrainPro – The Drain Fly Solution

Gary Mays from Whywait Plumbing has gone through this entire experience at his own home in the ensuite bathroom. Gary Mays also installed a DrainPro unit into the floor waste which prevents not only drain flies but also bacteria, odours and insects from exiting through the drain into the bathroom.

It is 3 years since he installed DrainPro units in all of all bathroom floor traps and they have completely eliminated the annoying tiny flies.