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Thread: sewer gas from basement shower...

  1. #1
    DIY Senior Member coach606's Avatar
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    Default sewer gas from basement shower...

    Two things happened the other day:

    1) huge rainstorm
    2) my main vent pipe in the house was stuffed with a rag by a construction crew in the attic.

    And I guess a third thing, the basement shower started to leak sewer gas. I put a wet rag over the drain and the smell went away. The toilet and lav in the bathroom are fine.

    I'm guessing something is siphoning the trap. But I believe this group is vented from a second 2" vent that also vents our kitchen sinks. I don't really know. The guy who put this bath in was not a plumber.

    Should I snake the drain? I uncapped the main vent and ran some more water in it to fill the trap. We'll see if that helps. It seems to have stopped the major smell, but the trap always smells a bit funky.

    Any ideas? I suppose it's possible this bathroom has no vent at all, but I believe it hooks into the vent for the kitchen group. Certainly it has no separate vent of its own.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    To work properly if there is a vent, it would need to run up above the flood rim of those drains connected above it or have its own run to the roof. There could be one, but it is not installed properly and the trap is getting siphoned dry in certain situations. Even if some traps are vented properly, they may not be vented within the proper distances which can also create problems. Any way you can tell how it is installed, or would you have to tear out walls?

    Some installers take a shortcut when building a shower on a cement slab and either omit the liner, or don't install it on a presloped floor. This allows moisture to filter through the grout or cracks and either continue into the slab floor or pool in the flat liner. After awhile, that trapped water can start to smell like a swamp, which could also account for some smells.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Senior Member coach606's Avatar
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    Default What I know...

    What I can see is that the group appears to be wet vented about three feet away from the kitchen sink above it.

    But you're 100% right about the water leakage. A year ago I popped the crappy plastic drain off to replace it with something nicer. It was rigged up with rubber gaskets and caulk and whatnot. He did it wrong and had to cut the top of the p-trap to make it fit. It just slid into a gasket and had some caulk on it. Worked okay until I tried to replace the drain, but quite a lot of water got under the pan.

    It's a pre-fab pan, by the way. No liner. It always smells a bit funky in there. But it's a small bath with no exhaust fan and has had some water leakage in the past.

    This sewer smell was really strong. I took the rag out of the main vent pipe in the partially torn up attic and ran some hot water into the drain. I'm going to pop the drain and snake it. I can actually see a small pile of gunk right in the bend. So maybe the partial blockage is causing it to siphon.

    Smell is quite a lot better. Shower stall is really a cheap thing. Once I get some time I'm going to knock it out of there and build something nicer. But I don't think I ever want to cut the cement floor so the messed up, cut p-trap may have to stay.

    I'll let you know if the problem returns. Thanks for the reply.

  4. #4
    DIY Senior Member coach606's Avatar
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    Default No ptrap at all!

    Closer inspection suggests that there is no trap under the shower. It's hard to believe that someone who could build the entire bathroom group under the slab didn't put a p trap in. But honestly, I can't see any water in it at all. It just looks like an elbow.

    Here's the guy's drawing. Looks like I need to beat the shower stall out with a sledgehammer and see if I can install a trap. I think the slop drain in the laundry room also has no trap.

    I mean, is it possible that there is a trap farther down the line or something? I only had sewer gas that was noticeable that one time with the heavy rain.

    I'm thinking no. But it's hard to believe no trap is there. Check out the drawing. Guy didn't even use wyes for drainage.
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    Plumber Cass's Avatar
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    B4 I finished reading your post I was going to ask how you knew there was a trap under the shower .

    You said "It's hard to believe that someone who could build the entire bathroom group under the slab didn't put a p trap in." I see it all the time.

    The tip off was when you said "The guy who put this bath in was not a plumber."


    There should not be a shower trap anywhere else but at the shower drain, running traps are not allowed.

    Adding a trap to the utility sink should be easy. As far as the shower goes if the shower is used only once and a while you could use a drain plug when it's not being used unless you get sewer gas when taking a shower.

    Because someone can glue pipe together doesn't mean they know how to plumb correctly. Hire a plumber and get an inspection to be sure all is done right the next time. Tearing up the concrete is the only way to add a trap to the shower drain. His drawing does not show any traps. It looks like you may need to add vents also, if you tear up the concrete. It shows him using Ts where there should be Ys being used which may cause problems down the road with clogging. If you ever have to snake it you may not make the turns and if you do it may be going in the wrong direction. This looks like a handy man mess to me. How long have you been using it this way?
    Last edited by Cass; 10-06-2006 at 04:45 AM.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Default trap

    If he did not know enough to put a trap under the shower, could mean that he also didn't know he should not use a running trap, but the odds are that if you can't see water in the drain there is no trap. Have someone flush a toilet while you listen at the shower drain. If there is no trap you will hear the flush.

  7. #7

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    Sorry to threadjack: what's a running trap? Is it a trap further along a drain not associated with a fixture?
    (important note: I'm not a pro)

  8. #8
    DIY Senior Member coach606's Avatar
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    Default There's no trap...

    There's no trap. I mean, it's not pictured in his drawing and I shoved a snake in there and it went three feet before hitting anything at all. I can hear the toilet flush with my ear three feet from the drain.

    I'm going to try to make some time to redo the shower pan. I was thinking that I could beat the shower pan out with a sledgehammer, break up the cement around the pipe and put in a p-trap. Then I'd build a custom shower pan and tile the walls instead of using a shower surround. I'll have to research building the pan (I've looked at it before) but I'm hoping I won't have to break up too much of the cement he set the pre fab pan on. I'll just make the new pan slightly higher than the old when I scrim the cement.

    I'm also thinking that I'll open the wall behind the lav where he has that capped pipe and put in an AAV. I know it's not code, but I figured I'd see if it worked okay for now. Next summer maybe I'll have time to run that to a vent going thru the roof.

    What do you think of my plan? I will never hire a non-licensed plumber again. If I have any money after our current attic remodel, I'll hire a pro to do it up right down there and relieve me of my worries.

    Anyone have a good link for some shower doors or other creative solutions in that arena? What we had was pretty cheap and unusual, an oddly sized neo angle shower.

    Thanks for the advice everyone. I've got a rag stuffed in the drain for now.

  9. #9
    Retired Defense Industry Engineer jadnashua's Avatar
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    Checkout www.johnbridge.com , you'll get all of your questions answered there. There are also some very good articles in their "Liberry" you should read for reference, then ask specific questions. They'll take good care of your shower questions.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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