Water sucked out of tub trap when sink is emptied

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    • #279504
      MasterPlumbers
      Keymaster

      I have a 90 yr old house with semi-original drain plumbing in the bath. The drain lines are all original, just the traps and feeds to the drain lines are new. The tub is about 2 ft from the stack and the lav is about 8 ft from the stack. I think the tub drain joins the sink drain about 1 ft prior to meeting the stack. The problem I have is that when the sink is filled w/ water and then drained, the water is sucked out of the sewer trap and then you can smell sewer gas come up out of the tub drain. I assume this is a venting problem, but i’ve run a snake down the stack from the roof and it seems clear. One other piece of info — I’ve also noticed that sometimes when the sink is drained, it backs up into the tub a little — this seems inconsistent w/ the problem I have, but figure I should mention it. Any ideas on what the issue could be? Are there easy ways to fix it (that don’t involve putting a new vent through the roof)? Thanks.

    • #301046
      Retired plbg1

      .Sounds like the sink drain is partly stopped, and that long sink run causes a vacum and syphones out the tub trap. You need some kind of relief vent in that sink line. Is that all thata on the stack is the 2 fix. If so cut a tee in the sink line and connect pipe to the stack. You might try one of those studo vents, its a Mechanical vent you put in the pipe line. But they give you trouble later on so make sure you can get to it for future repair.Let me know.



      Art retired plbg

    • #301047
      Retired plbg1

      The way you describe the pipe work is the way they did it in 1900, they had an S-Trap on the lav. and a drum are salem bath trap on tub, try having it cabled out to stack if that dont work you need a vent. Let me know. If you need drawing let me know.



      Art retired plbg

    • #301048
      hardycm

      Thanks for the replies, Art. So you think snaking out the drain could help? I sure hope so, as I’d hate to have to chip up tile to put a vent on the lav. Is there another way to provide a vent without doing that? I.e. what about something similar to what is done on a kitchen sink in an island?

    • #301049
      Retired plbg1

      Thats called a loop vent, but it has to be installed right are it wont work. Did you check out those stuor vent, its a mechanical vent you buy at box store, some places they are not legal. If you have a S-Trap you can buy a vented S-trap to replace and run a vent up from there through roof.



      Art retired plbg

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