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Thread: vent stack covered?

  1. #1
    DIY Junior Member sciguy2902's Avatar
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    Default vent stack covered?

    I have been in a 30 yr old home for the last 6 years and recently notice a sewer smell in the bathrooms. The septic tank is near a garden and has mint plants growing on top of the tank. My wife and I pulled weeds and thinned out the mint plants and that evening both toilets smelled of sewer gas. They were fine after one flush. About a week and a half later I noticed the smell as I started to shower, definitely coming from the drain. It has been several days with no further incident. Is this cause for alarm? Could we have disturbed something around the septic tank that caused the odors? Could it settle down on its own since we have had no trouble for 6 yrs?

    I am even more puzzled by what I found when I checked the vent stack exiting the roof... there wasn't one! I went into the attic and discovered that the vent is covered by the tin roof. The original roof was asphalt shingles which the previous owner covered with tin when the old roof wore out. It looks like the vent pipes for the sewer and the gray water system were cut flush with the asphalt and the tin roof laid over the opening. It has worked fine for 6 yrs so should I mess with it? Could this have something to do with the odors?

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    The reason the vent extends through the roof is to disperse sewer gas up in the winds. Otherwise that is prevented and it came come back inside an open window.
    The vents should be open and clear. A closed vent can allow traps to siphon dry.

    There isn't anything you can mess up on the outside near the septic. The pipe is underground, and you would have needed to break the pipe to harm it.

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    Moderator & Master Plumber hj's Avatar
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    I had one customer with a vent like that, and the "downdrafts" of air in the wall was pulling the odors into the rooms. If it is "venting" into the attic, there is no way to predict what could happen as far as sewer odors are concerned, BUT "pulling weeds" has NOTHING to do with your problem.
    Licensed residential and commercial plumber

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    DIY Junior Member sciguy2902's Avatar
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    It didn't make sense that I could have done anything outside by the tank, guess it was just a weird coincidence.

    When I smelled the sewer gas in the shower all the windows were closed. It definitely came from the drain in the tub. The other time the smell was at the toilet in bathrooms with no windows. Maybe there was a gap between the vent and the tin on the roof that allowed enough air for the vent to work although I never smelled any gas in the attic. Perhaps the roof/house settled a bit causing the tin roof to sit on the vent directly and prevent the air flow. Either way the first order of business is certainly to get those vents above the roof.

    Thanks for the info folks.


    Quote Originally Posted by Terry View Post
    The reason the vent extends through the roof is to disperse sewer gas up in the winds. Otherwise that is prevented and it came come back inside an open window.
    The vents should be open and clear. A closed vent can allow traps to siphon dry.

    There isn't anything you can mess up on the outside near the septic. The pipe is underground, and you would have needed to break the pipe to harm it.

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