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Thread: Adding new sink drain to existing horizontal drain

  1. #1
    DIY Junior Member Bob Lewis's Avatar
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    Default Adding new sink drain to existing horizontal drain

    The image below shows the current in-wall plumbing viewed from the laundry room (note that outlet has been moved). Opposite the wall is a bathroom and the drain pipe in question is connected to a sink in the bathroom. The connection from the drain stub in the bathroom to the drain in the wall is a 90 deg elbow. The section of wall on the left not open is where the drain enters a vertical drop with the vent line going up. My question is what would be the appropriate way to connect a new drain line for a sink to be installed in the laundry room. The level of the top of the sink in the bathroom is ~31" and the sink in the laundry room will be at ~37". Thanks in advance for any advice.
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  2. #2
    DIY Senior Member kreemoweet's Avatar
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    To begin with, if that is an 1 1/2" drain, then there is no appropriate way to connect a laundry sink, which requires a 2" drain. If it is 2", then you could
    cut in a 2x2x1 1/2 combo right above where the outlet box is to give you a new vent for the bathroom sink, which would rise to at least 37" and then cut
    over to the left to connect with the existing vent stack in the next stud bay. Just downstream of that would go a 2x2x2 combo to give you an inlet for the
    laundry sink.

  3. #3
    DIY Junior Member Bob Lewis's Avatar
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    The laundry sink isn't being used for the washer discharge. It is just for a simple sink in the laundry room. Does it still require a 2" line to add another drain to it? If so then will I need to add a separate drain for the laundry sink and plumb it into either the 2" or 3" line that is in the crawl space (along with adding the vent for the new sink as described above)? And wouldn't the new vent need to go to 43"? Seems like I read something about when the vent traverses horizontally it needs to be 6" above flood-plane. Thanks again for the help.

    And forgot to mention that I actually would like to have the drain on the right as opposed to the left.
    Last edited by Bob Lewis; 02-26-2011 at 12:21 PM.

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    Moderator & Master Plumber hj's Avatar
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    The sink only needs a 1 1/2" drain, but THAT drain is going to be too high to connect your sink into it, even if there were a simple way to do it properly, which there is not.

  5. #5
    Test, Don't Guess! cacher_chick's Avatar
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    Correct that one cannot drain both a lavatory and a laundry sink into a 1-1/2" horizontal line regardless of the washing machine.
    Correct that the vent cannot be horizontal until it is at least 3" above the flood rim of the highest fixture.

    Oops... I meant to type 6", not 3.
    Last edited by cacher_chick; 02-26-2011 at 05:59 PM. Reason: typo

  6. #6
    DIY Junior Member Bob Lewis's Avatar
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    Thanks for the replies guys. Looks like I will need to tie into the larger trunk lines below.

    Just for clarification not sure what you mean here that the drain would be too high. Are you talking the elevation of the drain if one were to tap into that horizontal line? The elevation of the sink drain from the floor is at 19". That cutout space is only 24" tall.

    Quote Originally Posted by hj View Post
    The sink only needs a 1 1/2" drain, but THAT drain is going to be too high to connect your sink into it, even if there were a simple way to do it properly, which there is not.

  7. #7
    DIY Senior Member kreemoweet's Avatar
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    In Washington, under the Uniform Plumbing Code, all laundry sinks require 2" drains. Of course, if there is to be no inspection, you can ignore this requirement:
    so many folks do. The new vent serves the lavatory, which you say is at 31", so 31" + 6" = 37". The new drain would only be too high if the laundry sink had an
    unusually low outlet.

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    Plumber jimbo's Avatar
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    I don't see in this picture how the vent to the left will connect and vent both sinks correctly.

  9. #9
    Moderator & Master Plumber hj's Avatar
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    A laundry sink, typically is ONLY 18" above the floor, so a drain line 19" high would be above its bottom. ALL laundry sinks have "unusually low inlets", just by their design and function.

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    DIY Junior Member Bob Lewis's Avatar
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    It will be inspected so it needs to be done right or not at all which is why I'm bugging you nice folks here on the forum.

    hj...This isn't a laundry tub. I'm putting in base cabinets that will have a 37" elevation to rim and the sink will have about an 8" depth so more like a typical kitchen sink.

    jimbo...vent is in area that hasn't been opened up yet.

    And I thought this was going to be an easy slam dunk. I have a couple of options I am considering and would like your opinion. Ideally I would like to have the sink to the right of the middle stud, but if not the left will work as well. Option 1 below would put the sink on the left. I would need to replace the current fitting on the vent/drain line to a double fixture fitting. This is probably the easiest. Option 2 would require replacing the vent/drain fixture with a 2" san tee, adding a double fixture fitting, running a new 2" drain line to the san tee, and adding a new vent line. I have a few questions about option 2.

    1. Since I only have the wall open on one side I would only be able to place nail plates on the open side. I'm guessing this isn't to code so I would need to open up the other side in the appropriate places and add nail plates?

    2. Are there any requirements around the double fixture as far as the length of horizontal runs or the vertical distance drop before you can go horizontal?

    3. This would require drilling new holes through the studs for the 2" horizontal drain line. This is a non-bearing wall so there is room, but what are the requirments as to how far away/how many holes you can have on a given stud? Assuming just adding another hole would violate code what are the options for adding structural integrity to the stud so it can be done?





    Option 1
    Name:  laundry_room_plumbing_option1.jpg
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    Option 2
    Name:  laundry_room_plumbing_option2.jpg
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  11. #11
    Test, Don't Guess! cacher_chick's Avatar
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    Your plumbing is fine if you add a cleanout below the tee.

    IRC Building code allows a 60% hole or a 40% notch in a non-bearing wall. A 2" I.D. pipe in a 2x4 doesn't work.

    What software are you using for drawing? Pretty nice.
    Last edited by cacher_chick; 02-27-2011 at 10:28 AM.

  12. #12
    DIY Junior Member Bob Lewis's Avatar
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    Using Visio for drawing. I just created those fixtures as shapes. If I end up doing more plumbing I may make up a whole series and pretty them up a little. I was thinking 2" would be 2 1/4" OD but I guess not. More like 2 3/8". So really the only option would be 1 assuming they make a double fixture that has 2" on one and 1.5" on the other? For the cleanout would that be a straight T or something like a long 90 or san tee?

    Or I guess I could use a double fixture with a 2" all around and go from 1.5" to 2" on the existing line?
    Last edited by Bob Lewis; 02-27-2011 at 10:49 AM.

  13. #13
    Test, Don't Guess! cacher_chick's Avatar
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    Since we have now learned that it is not a laundry tray, I am wondering if you can use 1-1/2 in the wall. I fall under a different plumbing code so don't know. Once of the other plumbers will need to advise.

    We usually use 2-9/16" bit for 2" pipe.

    The cleanout should be a cleanout tee.

  14. #14
    DIY Junior Member Bob Lewis's Avatar
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    Guess I need to get the lingo down. So what exactly is considered to be a "laundry tray"?

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    Forum Admin, Expert Plumber Terry's Avatar
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    A Lav can use 1.5" with a 1.25 trap or 1.5 trap
    A Sink uses 2" with a 1.5 trap

    If Washington State, if it's not a lav, it's a sink. What room is this going into?
    Also in Washington State, it's a double fixture cross, not a double santee cross.

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