Sewer flies

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by msk914, Oct 20, 2005.

  1. msk914

    msk914 New Member

    Hello all,

    I have a 100 yr old house. It has a full basement, in the corner nearest the sewer exit from the basement to the street it has a (mostly) unused bathroom. We noticed sewer flies this summer in that room. The plumber came over, opened the sewer access, and took the toilet off the floor, and there were many many flies. He cleaned the mess up, and then ran (with our agreement of course), a high speed water cleanup of the sewer line to the street. He before and after took pictures inside the line: It is very old and very full of holes from the trees. It is now clean, but a few flies are still seen. He has been out twice; we cannot find where they are coming from, although he thinks they may be sneaking past the wax seal on the toilet, or other places near the line. We want to kill them off, but he thinks (I might agree) that the sewer line should be replaced.
    Ok, the line goes under the slab. Also under our new porch. It is not feasible to replace, at least by ripping up the front of the house.

    Should we be thinking of relining the sewer line?

    Should we consider other ways to kill the sewer files? (if they are all around the holes in the sewer line) or maybe they are coming from elsewhere??? Should I call another plumber?


  2. Sewer flies are common with open ends into the sewer system without a trap to protect the sewer gases from entering. I would venture to say that there is a leak somewhere that is being overlooked, and I do not believe replacing your sewer line fixes the problem. A smoke test of the DWV system will decipher exactly where the sewer flies are coming from. Lack of use of plumbing fixtures is usually the #1 cause of this problem. Like a floor drain or sink that doesn't see much use and the trap seal evaporates inbetween uses.
  3. msk914

    msk914 New Member

    Re flies

    I assume DWV is shorthand for the valve one opens to get to the sewer line from the house....The room where the flies appear is a tiny bathroom. It has a door to a even smaller utility closet where the DWV is found. The plumber told me that the DWV (when he opened it the first time) had a zillion flies on the inside of the drain (and sewer line itself). He also found that the wax seal on the toilet in the small bathroom had a lot of flies on the 'other' side. 2 days ago, (and the number of flies has gone down to almost zero) he and I inspected both rooms and found no places where flies could get through into the room (unless they can swim up the toilet or get through the wax seal). Is this about a wax seal? Do these flies live in everyone's sewer lines?

    I have been telling my wife that they have to get into the house from somewhere, and the plumber, who is a working hand to a larger firm who we have used for many years and who seem to be honest people, he keeps saying ' they are small' they can get in through tiiiiiiny spaces.

    I think I will call him back for a smoke test. Or someone else.

    any ideas will be appreciated-- and thanks for the first message too!

  4. casman

    casman New Member

    New York
    Do a search on this site and the net for drain flies, they can come right through and a trap full of water which doesn't stop them, so its not a hole and a smoke test won't tell you anything...they breed on decomposing matter. My house is 1890 and I had them too...they are a real nuisance.....
  5. PEW

    PEW DIY Senior Member

    We have a summer home that, due to unusual conditions, we were not to for eight weeks. Toilet trap (1 gal flush) dried up and we had a fine collection of sewer flies last weekend.

    Our full time home, built in 69 will, on occasion, during summer months have one around.

    From what I know casman is correct in his comments.

    Last edited: Oct 21, 2005
  6. Good Choice msk914

    DWV stands for the Drain, Waste, and Vent system in your home. A smoke test is how you find leaks in a plumbing system without second guessing the situation or spending a great deal of time pulling toilets or otherwise. Age of a home is irrevalent in the case of having these in a home. If decomposing matter is anywhere other than the DWV system, I would consider those living conditions deplorable and not at the fault of the plumbing system. Sometimes traps do not provide the self scouring action needed to thoroughly clean them. If food waste is present, this is acidic and will sour over time. If you have an aging system, cracks, holes, or breaks in the system can be a cause of it. It's always best to follow the process of elimination theory which is the least expensive. Smoke bombs are $3 last time I bought them. :D

    Thanks for the follow-up!
  7. msk914

    msk914 New Member


    Sorry everyone, but now I am completely confused: They are not swimming up the toliet bowl, right? So I have a bunch of questions, I have read everywhere on the net, but I am still unsure about this:

    Is this a problem of cleaning them out of my sewer line (to the street) by cleaning all lines (or replacing them) --- we flushed my line with high pressure water, which it REALLY needed and then put organic waste killer down for a week, this has mostly but not completely eliminated them ---
    I have seen one or two a week since.


    Is this a problem of finding out how they are entering my house? (in other words is it impossible to eliminate them from my sewer line to street since we are all connected to the main sewer line in my town and they will just come back to my line)

    I have heard from a plumber (friend of a friend): Throw bleach down the line.
    Online they say: Buy DL5000.

    Anyone have experience?

    Thanks in advance,

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