I’m a bartender at a restaurant that is in an old gas station building. The floor drain that the sinks behind the bar drain into frequently smells like rancid meat farts, which is quite embarrassing when there are customers in the bar, but my boss has made no effort to try and figure out what the problem is.

I’m no plumber but have surmised that this is an issue with the floor drain either not having a p trap or it being messed up in some way. The trap couldn’t be dry from what I understand because it’s used frequently. I am wondering if there’s a way that this could be fixed that wouldn’t involve jack hammering the cement slab up, if I can determine whether there is a trap or not, etc. Currently I’ve been told to just dump bleach down the drain, which... doesn’t help.

Edit: There’s also an oatey sure vent air admittance valve, if that helps.

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  • Where is the air admittance valve? How could it be connected to the floor drain, ALL of its connections are under it, no.?
    – Alaska Man
    Jan 2, 2021 at 0:49
  • The air admittance valve is directly to the right of the floor drain, I’ve attached a clearer picture. That seems like it could be it, but I’m also reading that it’s pretty rare for them to fail? Never thought I’d be this intrigued to learn about plumbing! Thanks Jan 2, 2021 at 0:52
  • I have to charge my phone to take a flash picture, lol. But the valve comes straight out of the concrete next to the drain. Jan 2, 2021 at 0:53
  • Okay there it is! Jan 2, 2021 at 0:57
  • "Never thought I’d be this intrigued to learn about plumbing!" Lets put that to the test, unscrew the AAV and stick you nose over the pipe. Wash the AAV and see if the little flapper inside is still spring loaded.
    – Alaska Man
    Jan 2, 2021 at 1:06

1 Answer 1


The presence of an air admittance valve (AAV) implies a trap (since otherwise there's not a lot of point for a vent), but is then also the most likely thing to have failed such that things stink.

It can be replaced, and probably should be.

  • "The presence of an air admittance valve (AAV) implies a trap" It does?
    – Alaska Man
    Jan 2, 2021 at 0:57
  • Without a trap, there's no need for a vent, so yes, it does.
    – Ecnerwal
    Jan 2, 2021 at 1:17
  • Also, I stuck a plastic bag over the vent and ran the sink and it inflated. Which... is not what’s supposed to happen right? Jan 2, 2021 at 1:38
  • The bag should deflate, if anything. Despite the claims you have read, my experience of AAVs is that they can be relied upon to fail, and stink, and thus I will go to a lot of effort to provide a vent pipe leading outdoors rather than relying on an AAV.
    – Ecnerwal
    Jan 2, 2021 at 1:42
  • 1
    Gotcha! Thanks for explaining. So the smell is coming from the vent and would only be able to come from the drain with a vent installed if the vent was stuck shut or something, which I know it’s not because of the bag test. Cool! I think I can make a solid case for a new vent now. Jan 2, 2021 at 3:04

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