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Thread: Brand New House septic issue?

  1. #1
    DIY Junior Member plumbinggrappler's Avatar
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    Sep 2013
    New Jersey

    Default Brand New House septic issue?

    We've been in a newly constructed, large house for almost two weeks now. Last Sunday morning my wife woke in the middle of the night (2 am) and smelled a strong smell, and woke me up. I concluded that it wasn't propane, but rather sewer gas, but it was really strong. Sniffing around led to the conclusion that the source was somewhere near the master bath toilet (which is in its own small room). The other fixtures in the master bath area (large shower and large whirlpool tub) didn't have the strong smell near them. No smell from anywhere else in the other bathrooms or sinks upstairs or down.

    It took about 10 hours for the smell to go away.

    This morning (Tuesday), we got another "episode" of sewer smell in the same place. Contacted our builder for the second time (his first suggestion had been that possibly a trap was without water somewhere, but that wasn't the case...which I knew anyway). This time he sent a plumber out to replace the wax seal on the bathroom toilet. (Its a modern Kohler). He replaced the seal with a more heavy duty one with a longer flange and more waxy material. He was at a loss to explain the phenomenon. While he had the waste stack exposed, I leaned over close to get a sense of how strong the "normal" stack odor was, and it wasn't very strong at all....not strong enough at all to generate the smell we got.

    I'm thinking that I have some kind of intermittent septic problem coupled with a venting problem. It seems to me that I must have gotten two "burps", where the septic system somehow had a gas buildup over time that then was released all of a sudden and somehow partially vented itself out of the master toilet area...but nowhere else (in the house).

    This is a brand new house. Our septic system is new, and located substantially downhill in the front yard. I'm not sure what could be causing this, and maybe the new wax seal will stop the gas intrusion to the house, but it concerns me that we must be getting substantial gas "burps" that ought not be happening. How does septic gas normally exit the tank? Doesn't it just usually drift up the inflow pipe and up the vent system in the house? If so, it seems to me that what we've seen suggests that its being trapped somewhere until enough pressure builds up to blow it through the blockage, at which point the "puff" of gas comes into the house vent system with more pressure than you'd expect.

    Thoughts and suggestions are welcome. I think I'm going to call the builder and ask for the septic installer to come out, but I'd like to have some sense of what to ask him to do. Thanks.

  2. #2
    DIY Member philtrap's Avatar
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    Jun 2013
    Long Island, NY


    I'm no expert (as these guys will tell you), but isn't there a vent off of the main trap that leads to the septic system? If so, that's where the burp smells should go...

  3. #3
    DIY Junior Member plumbinggrappler's Avatar
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    Sep 2013
    New Jersey


    One other item that I left out.

    We initially thought that using the whirlpool tub might have had some effect on the first instance. I read something about draining a lot of water "pulling" water out of a toilet trap. So on Sunday afternoon we filled the tub and then drained it, and stared at the water in the toilet bowl while the tub was being drained. There was some motion (not sloshing, but more than just a little back and forth) in the toilet bowl water. I mention this because I just saw on another thread that motion of toilet water while other stuff is draining could be evidence of a clog somewhere.

    In our case, I believe the tub and shower drains enter the waste line just behind the toilet, through a horizontal "wye" connection. I believe this because the builder has another mirror image copy house going up and I've been going there to see how the sytems are set up before the drywall is installed.

    PS: I can't say that I know what a "main trap" is. My understanding is that every drain has its own individual trap, and each toilet has the trap built into it. If my house has a main trap, I don't know where it it.
    Last edited by plumbinggrappler; 09-24-2013 at 02:49 PM.

  4. #4
    DIY Senior Member Smooky's Avatar
    Join Date
    Apr 2011


    All of your drain pipes should be vented. The vent pipes go up through the walls and exit the house through the roof.


    Some fixtures may have an air admittance valve (AAV). The AAV are suspose to allow air in but not let sewer odor into the house. There should still be some roof vents to allow sewer gas to vent out so pressure does not build up and leak out.


    Here is a link to a sink trap with other good vent info:

    Last edited by Smooky; 09-24-2013 at 03:49 PM.

  5. #5
    Jack of all trades DonL's Avatar
    Join Date
    Mar 2011
    Houston, TX


    I would ask your neighbors if they have the same problem.

    The builder should fix it.

    The new houses are of piss pour design now a days, and it should not be your problem to fix it.

    But you have to live with it, and your wife.

    Good Luck.
    Theory only works perfect in a vacuum.

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