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Thread: How to tie into this main stack for small wet bar sink

  1. #1
    DIY Member kezug's Avatar
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    Default How to tie into this main stack for small wet bar sink

    I have a wet bar sink that I am putting in the basement. I have the hot and cold water lines all ready to go but I am now stumped as to how to connect my sink drain to this 4" inch waste stack.

    This sink is in my basement. The 4" line that you see below is a waste stack for my upper floors. It is one of two stacks that I have in my basement.

    My questions:
    1) how can I tie into this stack for a waste line from my sink that I want to put in?
    2) my sink is going to be right next to this 4" waste line. Will I need a Air Admittance Valve?

    NOTE: My sink will be to the right of my supply lines and to the left of that vertical soffit that the 4" waste from upper floors is located.

    Here are some pics:



  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    You will still need venting for the bar sink.
    When air and water come down the line, it has an effect on the water in the p-trap of the sink below. This has always been the case.

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    Test, Don't Guess! cacher_chick's Avatar
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    The first question is whether the drain and vent will fit in the outside wall to the inside of the insulation.

    That chase is pretty big and might afford you enough room to easily get a new vent up alongside the existing stack. If it goes straight up through the roof you could tie the two together in the attic.

  4. #4
    DIY Member kezug's Avatar
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    Quote Originally Posted by cacher_chick View Post
    The first question is whether the drain and vent will fit in the outside wall to the inside of the insulation.

    That chase is pretty big and might afford you enough room to easily get a new vent up alongside the existing stack. If it goes straight up through the roof you could tie the two together in the attic.
    There is no room...to get to the roof from this location. This is in my basement of a 2 story.

    Why cant I just put in an AAV under the cabinet (like for an island sink)?

    However, I am still in need to find out how to tie into the 4" waste that is showing inside that chase?
    Can I do a rubber clamped coupler above and below a sanitary tee?

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    Test, Don't Guess! cacher_chick's Avatar
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    The vent goes from the 1st floor to the roof, so one very well can go from the basement to the roof also. It's all a matter of perspective.

    Legally the use of an AAV would depend on your plumbing code. Talking to your plumbing inspector would be a good place to start.

    The problem with using an AAV under a sink in a basement is that every time there is the slightest backup in the line it will hit the AAV first. This contaminates the air check diaphragm and stops it from sealing. Then the house fills with sewer gas.
    If you must use an AAV, the vent should be piped up above the flood rim of the sink, where it will be less likely to ever become contaminated.

    You can connect the drain to a sanitary tee in the stack. You will need to make sure the stack is well supported when you cut it in.
    Last edited by cacher_chick; 11-19-2012 at 03:37 PM.

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    DIY Senior Member dlarrivee's Avatar
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    Quote Originally Posted by kezug View Post
    There is no room...to get to the roof from this location. This is in my basement of a 2 story.
    Sure there is, that other stack doesn't disappear, it goes up and out the roof.
    Quote Originally Posted by kezug View Post
    Why cant I just put in an AAV under the cabinet (like for an island sink)?
    You can do whatever you want, but using an AAV is a LAST RESORT not the BEST PRACTICE.
    Quote Originally Posted by kezug View Post
    Can I do a rubber clamped coupler above and below a sanitary tee?
    Why rubber couplings when you have plastic pipe? Of course you use a sanitary tee, I'm not sure what other details you're asking about?

  7. #7
    Forum Admin, Expert Plumber Terry's Avatar
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    Rather then a rubber coupling, they would be metal wrapped rubber couplings to prevent the pipe from shifting out of line. Mission makes them.


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    DIY Member kezug's Avatar
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    Quote Originally Posted by dlarrivee View Post
    Sure there is, that other stack doesn't disappear, it goes up and out the roof.
    Well, I will certainly check into seeing how I can run a vent line up and out the roof. Might have to tear out some drywall on floors 1 and 2 and then up and out the roof.

    However, it just kills me that the builder didnt run a couple pipes up and out the roof...especially since they plumbed for a bathroom. Dumb.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Normally if there is a bathroom rough in the basement, they would have dropped down a vent for it too.
    I have also gone to the next floor, found a vent and dropped that down.

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