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Thread: double sanitary tee vs double combination wye

  1. #1
    DIY Junior Member Jfknz's Avatar
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    Default double sanitary tee vs double combination wye

    Due to a tight squeeze between the floor and ceiling below, we installed a double sanitary tee (accommodating a toilet on one side and a shower on the other). Upon receiving the documentation for the toilet (Toto model MS854114S(G)/MS853113S) we discovered that they recommend against this and instead suggest use of a double combination wye (see page 2 of http://www.totousa.com/Portals/0/Pro..._MS853113S.pdf). Toto recommends wye in back-to-back toilet installations - which is not my situation as tee only serves one toilet and one shower.
    Has anyone had a problem (or success) using a double sanitary tee in a situation like mine?

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    The problem with doing it with back-to-back toilets is that the water from one toilet can shoot across and effect the opposite one. The shower drain does not flow as such, and should not be an issue.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    The velocity of the flushed water from the toilet is fairly fast...without the 'proper' fitting, it can shoot across to the other fixture (the shower). Probably not enough to come up in the shower, but it is a potential risk. It will also make snaking the line tougher as it may just go across rather than down.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    Forum Admin, Expert Plumber Terry's Avatar
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    It's going to mess with the shower. I would install a 3x2 wye lower down the stack for the shower and come up separately for the shower, and then revent at 42" above the floor.
    This is not a good plan what you have done.

    I would not put a shower opposite a toilet. Especially with the new ones that are using a 3" flush valve.
    Last edited by Terry; 12-22-2012 at 09:15 PM.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Depending on HOW you did the shower drain, NEITHER fitting may be "approved" or appropriate. The proper fitting would be a "back to back fixture fitting".
    Licensed residential and commercial plumber

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