First question, what is the black pipe in the picture above where the drain pipr goes into the wall?

Additionally, we have an intermittent sour smell coming from this bathroom. I replaced the wax seal of the toilet thinking that might be the problem. However it was not. Last night, the smell occurred again. After some investigation and wafting, i think I narrowed the smell to underneath the sink (hence the picture and post).

I guess the second question would be how do i get rid of the sour smell?


  • What, you didn't like the answers you got at imgur? Apr 13, 2017 at 17:36
  • Well, first, two different communities/audiences. Second, I didn't expect to get answers, let alone useful ones, from imgur. Last time I posted here, I posted pictures to imgur, and linked them here because I thought that's what I had to do. Still new when it comes to posting with photo examples.
    – Russ
    Apr 13, 2017 at 18:24
  • If it's a sewer gas smell then I'm guessing someone thought they could vent the drain into the sink cabinet. Is this bathroom original to the house or did someone add it? Is there an attic above this room where you can see if there's a vent that goes up? Apr 13, 2017 at 19:24
  • @PlatinumGoose It is an added bathroom that was done as part of a garage conversion prior to my moving in. I don't recall seeing anything in the attic/crawlspace resembling a pipe going up through the roof. It was suggested that maybe the vent goes under the insulation and vents under the eve of the house. I'm not sure if this is something that is done in practice of a one-story home.
    – Russ
    Apr 13, 2017 at 21:17
  • 1
    No way to tell what it is thru the internet but i would put a check vent (air admittance valve) on it. A one way vent that will allow it to draw air in but keep sewer gas from escaping into the room.
    – Alaska Man
    Apr 14, 2017 at 1:37

1 Answer 1


I seemed to have fixed this issue with a 90 degree elbow to fit over the pipe that comes out of the wall, and an Air Admittance Valve that I put on the other side of the elbow pipe. No glue or tape was necessary.

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