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Apologies if this is the wrong forum to post this question. Our house has a vent pipe in the basement coming off the main stack (water line going to sewer).

I understand there is a pressure difference created during a flow (from flush or sink water) but why is the vent in the basement? Or is there one on the roof as well? Should I be concerned there will be runoff or splash-back in the basement in case the pipe is blocked?

The flexible tube sticking with the cap was recently added because of some splash back that occurred due to a blockage at the bottom junction. I'll let you know the model of the cap but I believe it is something similar to a plastic version of a Gizmo vent cap. I'll edit when I know the exact model. Since this installation, I haven't noticed any more runoff coming out.

Snapshot of Basement water line with vent pipe

  • Chances are the upper wye leads to a vent, or the 3" line is also a vent. Have you traced them? – isherwood Jan 12 '16 at 16:29
  • Thank you for the suggestion. It is possible the upper wye leads to a vent though I have not traced them. I think it is more likely to be a sink in a bathroom on the third floor. Is there any way to trace them easily? Perhaps I can turn on a sink and listen in the basement for percolating noise. I think you are dead on when you mentioned the 3" line could be a vent because I do know there is an open copper-like pipe coming out on the roof. I may be mistaken though. – rshroff08 Jan 13 '16 at 23:50
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Are you talking about that flexible tube sticking off to the right? It's not a vent pipe. It's a poorly done drain for something like a clothes washer or a water softener.

I suggest pulling that flexible tube out, scraping off the black crud, and gluing in a short piece of PVC pipe and a cap.

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    No matter what you should cap that off: it's direct entry for sewer gasses (like methane) into the basement. Right next to what looks like a gas water heater. That needs either a cap or to be done properly (P-trap, vent). – gregmac Jan 12 '16 at 16:41
  • Thank you both for excellent details. This was very useful. Some more details: The flexible tube sticking with the cap was recently added because of some splash back that occurred due to a blockage at the bottom junction. I'll let you know the model of the cap but I believe it is something similar to a Gizmo vent cap. I'll edit when I know the exact model. Since this installation, I haven't noticed any more runoff coming out. I am little concerned that sewer gases may pose a risk. Do you think the vent cap is not sufficient? I do know the vent cap opens only on pressure change. – rshroff08 Jan 13 '16 at 23:48
  • What vent cap? There's no vent cap there. – longneck Jan 13 '16 at 23:52
  • Oops, sorry! You're right. I am starting to realize I might be in over my head and probably should call a plumber because I remember a few days ago I had a sewer-gas like smell in one of the bathrooms (though that might be an issue with a trap in the plumbing in the bathroom itself). If I were to try to cap this myself, what brand of vent cap would you recommend? Thank you again for all the help. – rshroff08 Jan 14 '16 at 15:48
  • You don't want it to vent. You just want to cap it. – longneck Jan 14 '16 at 15:54

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