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Thread: bathroom vanity drain to vent stack question...

  1. #1
    DIY Junior Member Iforgot's Avatar
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    Default bathroom vanity drain to vent stack question...

    I bought a house built in the early 50's for a fixer-upper for myself. The Vent stack is 3" PVC running straight vertical from the crawlspace which is connected to cast iron. I can not relocate the stack under the floor of the bathroom as it is next to cement foundations on 3 sides. The kitchen sink, the toilet, tub, and bathroom vanity all drain into this stack under the floor directly under the bathroom. The issue is that the stack coming up into the bathroom is 18" in from the one wall. I wish to try and reclaim some of that space by a couple 45's in the stack just above the floor in the bathroom, back to the wall, then up 6' into a couple more 45's to put me back at my existing roof exit for the stack. The problem is the vanity drains into the stack 1' above the floor. I would "like" to start the 45 in the stack as close to the floor as i could (if I can) so I can put the vanity over top to reclaim the space, but can I drain into the stack if the 3" 'y' connector is in the 45 degree part of the stack, not the vertical part?

    I have attached a simple paint drawing illustrating what I mean, the red circled area is what's in question because it will not drain into the stack at vertical.

    The second image is a top down of the current bathroom layout, I'd like to move the tub and Vanity back towards the wall about 8" to gain some more space.

    If I can not do this then unfortunately because of all the obstacles in the way in the crawlspace I will have to leave the existing wall that was built to house the vent stack in place and lose out on some extra space.

    Thanks for any input and/or recommendations!
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  2. #2
    Moderator & Master Plumber hj's Avatar
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    I cannot see how you could gain ANY space if the pipe comes through the floor in its original location. To gain space, you would have to move the entire pipe backwards, and that would have to be done UNDER the floor. If the black line labled "vanity" is supposed to be a drain line, there is NO fittlng that would legally make that angle.
    Licensed residential and commercial plumber

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    DIY Junior Member Iforgot's Avatar
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    Well the vanity sink would move back 8" putting the sinks down drain exactly over top of the stack vent where it comes up from the floor, however, i would have to 45 the vent at the floor. The space under the vanity is not important so if I have to modify the cabinet but it's not important to me if I lose a place to store my toilet bowl cleaner and accessories under the sink. It's a cabinet vanity.

    But that is exactly what I wanted to know was if there was a legal fitting to make that attachment circled in red, the black line labeled vanity/sink would be the drain line, this would be P trapped of course.

    Thank you for your reply, it helps tons. It was actually an argument with my wife, I was saying that I can 45 the vent stack but it has to be above the wet stack, which means it would be above the vanity's drain and in effect too high to move the vanity back anyway, so whats the point of moving it back. She wants me to 45 right at the floor, so the stack goes to the left and back to the wall, but that puts the vanity's drain location in the area on the 45 angle, which I can not legally do.

    Another question, could I drain into the bathtub, or toilet lines if I redo the Vanity's drain to not go directly to the stack, but rather down through a new hole and tie into an existing drain from the toilet or bathtub. Both these drains run near under the floor in the crawlspace, pretty much exactly as depicted in the first image.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    quote; Well the vanity sink would move back 8" putting the sinks down drain exactly over top of the stack vent where it comes up from the floor, however, i would have to 45 the vent at the floor

    Put the drain directly below the sink drain would create an almost impossible situation to connect the sink drain. You COULD connect into the 45 drain line, but it would create a major piping situation for you, and would probably NOT be able to be done INSIDE the cabinet. You are probably in over your head, and may need a plumber to accomplish it.
    Licensed residential and commercial plumber

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    DIY Junior Member Iforgot's Avatar
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    You are probably right hj, i think the best bet is to just leave things be and get a plumber in. thanks again for your help.

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