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ticklmetan 08-26-2011 03:14 PM

Sewer Flies - Help Locating Breeding Site
I have a two story home with a basement. Last year, we had a sewer fly infestation throughout our home. We sent the bug samples to an entomologist who identified the flies as phorid flies, which I know are usually associate with sewage leaks. He didn't think we had a leak as he said a leak usually produces an immeasurable number of flies. And, he thought we didn't have nearly as a many flies that are associated with a leak. He said that it appeared that our trap had dried out in our basement shower (which had never been used since installed), and the flies came in through there and propagated throughout the other drains in our house. So, he recommended flushing the basement shower drain with water to fill up the trap as well as taping and cleaning the other drains/garbage disposal to locate the source and eliminate those flies, which we did. I also got rid of all my indoor plants.

Within a week, we had a significant reduction in our flies. When I say significant, we would see a fly or two every other day, where we used to sit around smacking our legs, face, eyes or swatting all day. So, we thought the flies were just taking a while to die off. When the fall temps became colder, our fly problem disappeared.

Fast forward to July of this year, the flies have come back. But, not nearly as many as last time since we have kept up on keeping our drains clean and our trap filled. We may see a fly here and there. Like maybe one fly a day or every other day. But, I don't want to see any flies at all, except maybe a occasional house fly following us inside. These phorid flies are a nuisance.

So, now I am worried about a sewage leak. We did have a full bathroom put in the basement like 5 years ago, and had to dig up the floor to install it. Now this was done by a remodeling company and plumber with the proper permits and all -- not a do it yourself job. The sewer pipes are your standard PVC not clay or cast iron.

My question is wouldn't we see lots of flies with a sewage leak not one or two. And, wouldn't we see them all year long? These seem to go away in September when it gets colder. It makes me think that the flies are coming from outside somewhere and finding there way in through the foundation or walls since they only show up when it's warm out. At this point, I am not sure what direction to go to figure out where they are coming from. Hoping for some assistance or directed advice on where to start, so I am not just throwing money at different things only to come up with nothing.


PAbugman 08-27-2011 11:29 AM

Phorid flies can be very tough to locate unless they are very bad. I donít suspect a sewage leak, although that must be on the list of considerations. A sewage leak generally brings sewer flies (psychoda). Phorids (humpbacks) flies do like damp, rotting organic material. Consider:

Toilet not tight on gasket/floor. This is not a sewage leak per se, but Iíve seen phorids enter this way.

Air conditioning condensation drain going under slab or accumulating somewhere undetected.

Sump pumps in basement floors, even if covered.

Overflow drains, if any, in basement sinks, tubs.

Even though you are now using all basement drains, maybe there is enough scum above the waterline to provide breeding habitat. Try a good cleaning of same. A good thing to put in unused drains is mineral or baby oil. It does not dry out nearly as fast as water. Donít use vegetable oil-it goes rancid.

Does you basement bathroom use a pump to lift the waste to your sewage pipe? If so, is the pump well and properly vented to exterior?

Just some quick thoughts; if I have more Iíll get back to you.

ticklmetan 10-05-2011 11:07 AM

Thanks PABugman for your response!

Here's a new update. Yesterday, our sewage backed up into our basement shower again. :( We are having a plumber TV the line to see eactly what's going on since they couldn't find anything from mere inspection. County says their end of the lines are open and flowing. Plumber thinks our bugs are likely related to the sewage issue, and it's possible it could be a slight break in the line since it appears the line is open and clear water is flowing through it. Or, if it's not a break, it may be a blockage in the main line. If the latter is the case, I would imagine the flies are coming from somewhere else? Plumber also mentioned something about a broken wax ring in the toilet that could also create a breeding ground for flies.

With regards to the overflows, I think we are all clear there. I would doubt the shower has any scum above the water line since no one has ever taken a shower in it since it was constructed. Shower has only ever seen bleach and water.

Not sure if our basement bathroom uses a pump to lift the waste to our sewage pipe. I would say no. Plumber did mention something about checking for to see if a backflow valve was installed. Is that the same thing?

By the way, flies seem to be gone...but the weather has gotten colder.

DangerMouse 10-05-2011 11:12 AM

One tip I saw here may help you. Add a little veggie oil to that shower drain to help keep it from evaporating from non-use.


PAbugman 10-09-2011 10:36 AM

Make sure the shower drain is always full of water, or use mineral/baby oil as it doesnít dry out. Sewage pipe leaks and broken gaskets will give an avenue to these guys as well.

Iím sure that you donít have a sewage lift pump or you would know it as it would be visible and audible. Backflow preventer valve is always good to have, but has no bearing on flies.

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