Back to back toilets in horizontal main

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by tmcnutt18, Dec 4, 2019.

  1. tmcnutt18

    tmcnutt18 New Member

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    I have back to back bathrooms that are a mirrored image of each other. The main line will start beneath the bathrooms and be a horizontal line that I would like to keep in the floor joist space. I'm trying to figure out how to plumb the toilets. They are back to back. I'm thinking the first toilet would be a 4 x 3 closet bend into the main, then a 3 x 3 x 1.5 Wye with a 1.5" street 45 for the vent up the wall that divides the bathrooms. Should I use a 3 x 3 x 3 Wye with a street 45 to pick up the next toilet? How can I connect 4" toilet line? What about vent for this toilet? Could I do another 3 x 3 x 1.5 at a slight angle from horizontal over to the next joist space and then back to wall between bathrooms?

    Thanks,
    Tom
     
  2. Terry

    Terry Administrator Staff Member

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    One 2" vent would vent both toilets. I would use wye fittings. You only need 3" and they make 4x3 closet flanges. Toilets typically have a 2" trapway dropping into a 3" line.
     
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  4. tmcnutt18

    tmcnutt18 New Member

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  5. tmcnutt18

    tmcnutt18 New Member

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    Terry,

    Thanks for replying. Can the vent be between toilets so I can run vent up dividing wall? See attached drawing that lists fittings. Let me know if this would work. Do you recommend Wye and street 45 instead of long sweeping one piece wye?

    Thanks,
    Tom
     

    Attached Files:

  6. WorthFlorida

    WorthFlorida When the wife won't let you get a Harley!

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    Yes, the vent would go straight up on the center. Reduce it down to 2".

    Screen Shot 2019-12-05 at 1.44.40 PM.jpg
     
  7. tmcnutt18

    tmcnutt18 New Member

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    I don't think I have enough room to use a double Wye and keep main line in joist space.
     
  8. Reach4

    Reach4 Well-Known Member

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    See back to back bathrooms on the lower left of https://terrylove.com/forums/index.php?attachments/upc_wet_venting_bathrooms-jpg.34573/

    That would satisfy UPC. Kentucky State Plumbing Code is based on an IPC precursor, so KY code would probably be more permissive. Current IPC is more restrictive than UPC in one area that I know of: they would want the pipe below the lavatory to be raised from 1.5 to 2 inch and the wet-vented section carrying the shower water to bump to 3 inch.

    I suspect your dry vent diagram is fine, except that I think that instead of a tee, that would be a 3x3x2 wye+45 or combo. I think that is to minimize getting solids into the vent.
     
  9. Allison

    Allison New Member

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    Are these double wye/ 1/8 bend fittings readily available? I am having trouble locating these at the box stores, only finding double fixture fittings which look slightly different (to my untrained eye at least).
     
  10. Reach4

    Reach4 Well-Known Member

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    You want ABS I presume.
     
  11. Allison

    Allison New Member

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    Yep, I want ABS
     
  12. Reach4

    Reach4 Well-Known Member

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    I am not finding that so far. You can use a double wye [​IMG] and two street 45s.

    A double fixture fitting would be nearly as good, and is easier to find. [​IMG]
     
  13. Allison

    Allison New Member

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    Are there online suppliers that carry the double wye/ 1/8 fitting? Everything I've found looks just like like a double fixture fitting. I was under the (maybe wrong) impression that the wye+45 and double fixture fitting wouldn't pass UPC for back to back toilets.
     
  14. Reach4

    Reach4 Well-Known Member

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    All that carry much in ABS would have a double wye and two street 45s. That would be best.

    Two combos or wye+45 in series might do what you need and then a combo for the vent.

    Are you planning to have the output of the dual whatever in the horizontal plane or vertical? I am not confident that a double whatever adds much for you.
     
  15. Allison

    Allison New Member

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    I'm planning on using it in the vertical plane, something like this:
    upload_2019-12-11_12-40-44.png
     
  16. Reach4

    Reach4 Well-Known Member

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    So that mounted vertically would have an elbow at the bottom to go from vertical to horizontal. I have to think there would be a better way.
     
  17. Allison

    Allison New Member

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    Yeah correct, I am limited on space. I am planning on running a horizontal drain perpendicular to the joist direction then connecting to the main stack. I'm trying to keep the connections to the horizontal drain as much in the joist space as possible (so the wall that will eventually hide the drain does not have to be exceptionally wide, this is in a currently unfinished basement). I've considered using two wyes in series but then it is tight to keep them in the same joist as the toilet drains, and tight again to find a spot to vent before the next connection (shower and tub). It might be possible but I'm trying to explore all the options/make sure I can source all of the potential fittings.
     
  18. Reach4

    Reach4 Well-Known Member

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    In the downstream joist bay, I am thinking of a wye somewhere between horizontal and tilted 45 degrees. Maybe a 4x3 closet bend coming down, and a 45 or 22.5 to make those things connect.

    Maybe make a top view sketch showing the closet flange locations and the joist locations. Somebody may have the better suggestion based on that.

    You could buy some smaller fittings to play with as a model of what you implement. Perhaps sand those smaller on the ends to fit together easily for visualization.
     
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