Double wye used for double vanity

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by xr4ti, Aug 5, 2013.

  1. xr4ti

    xr4ti New Member

    Joined:
    Dec 23, 2008
    Location:
    Wisconsin
    Hello everyone -

    I've been visiting my new home daily as construction progresses, and the rough plumbing started last week. I noticed that they have used double wye's in the upstairs bathrooms, both slated for double vanities. I have seen and used the double fixture fitting in past projects, so I am wondering if there is any difference here? Thanks.

    [​IMG]
     
  2. asktom

    asktom Member

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    Location:
    Victor, MT
    It should be a double fixture fitting. A double wye creates a double S trap. A double fixture fitting is made so that air in the trap arm meets the stack before the drain drops down so that a siphon cannot be created. If the trap siphons it breaks the trap seal and there is nothing between your nose and whatever gas is in the sewer. An exhaust fan in the bathroom makes the situation worse.
     
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  4. hj

    hj Moderator & Master Plumber Staff Member

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    Doulbe Ys and 45s create "3/4 S traps" which are just as bad, and illegal, as full "S" traps. The ONLY fitting you should use is the back to back one, and NOT a sanitary cross either. A "plumber" who makes an installation like that has no concept of plumbing hydraulics and should go back to school for a season or two, if he ever went to school.
     
    Last edited by a moderator: Apr 4, 2015
  5. xr4ti

    xr4ti New Member

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    Dec 23, 2008
    Location:
    Wisconsin
    Thanks for the input, glad I asked here.

    I'll bring this up with my builder tomorrow. Rough inspection is next week and I'm not confident they will flag the fittings.

    Here's another pic. Looks like it's been bouncing around in the bottom of a DWV bin and they finally found a place to dump it. My house!
     

    Attached Files:

  6. Terry

    Terry Administrator Staff Member

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    Occupation:
    Plumber
    Location:
    Bothell, Washington
    When you combine two lavs, it requires a 2" drain.
    It should have been a 2.0" x 1.5" x 1.5" x 1.5" double fixture fitting.

    So not only is it the wrong fitting, it's also undersized.
     
  7. Hammerlane

    Hammerlane Member

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    Location:
    Ohio
    Kind of resembles this:
     

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  8. Hammerlane

    Hammerlane Member

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    Ohio
    A few more
     

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  9. hj

    hj Moderator & Master Plumber Staff Member

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    ON my screen it looks like a 2" riser with 1 1/2" arms. IF so, it is just the wrong fitting.
     
  10. as20worm

    as20worm New Member

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    Apr 3, 2015
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    Ohio
    I know this is an old thread but had a couple questions related to this exact thing I found while doing an internet search. 1) why is a 2" drain required if the value of each lavatory is only 1 unit and an 1 1/2" pipe can serve a value of 2 units? Please specify where I can find this is in the code book. 2) Where can I find in the code book that the wye combo is not allowed because of the venting issue it creates by forming a partial s-trap? Does that same concept also apply to a laundry drain trap when it connects horizontally to a vertical drain / vent? Is it in the code book that that fitting should be a sanitary tee to allow for the proper venting and not a wye combo? I would like to have direct code specifications so that I can point them out to my plumber who thinks he is right just because the building inspector passed his work. Thanks.
     
  11. xr4ti

    xr4ti New Member

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    Location:
    Wisconsin
    And to update my own thread - I still have the double wye's, the plumber never changed them to double fixture. I brought it up to the building inspector and this is what I was told:

    I talked with 2 master plumbers who have been around since the 70's and both say the wye with a 45 is ok. There is some info on the internet that disagrees and references the Uniform Plumbing Code which Wisconsin does not adopt. I will keep digging. Pulled the following off the internet from a master plumber?

    "The Y or a combination Y-1/8 bend can be used ANYWHERE. It is the sanitary tee that has its usage restricted to vertical lines when used for drainage, (not venting), purposes."
     
  12. as20worm

    as20worm New Member

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    Thanks for the update, notice any issues since you have been living with this install?
     
  13. hj

    hj Moderator & Master Plumber Staff Member

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    QUOTE; "The Y or a combination Y-1/8 bend can be used ANYWHERE
    That is true as far as it goes
    , but anyone who says it can be used for an unvented trap arm is completely ignorant of the hydraulics involved. NO "competent" inspector would EVER approve it, and it has NOTHING to do with which code is involved, because it is a law of physics, NOT a plumbing code issue. (unless it is the IPC "code" which basically allows any thing). Looking at the picture again, it looks like a 2" system until it reaches the cleanout then it changes to 1 1/2 with a bushing on top of the cleanout, BUT, that does not make it any "righter".
     
  14. Tom Sawyer

    Tom Sawyer In the Trades

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    The wye and 1/8th bend can possibly put the trap weir above the drain inlet which makes the trap susceptible to siphon age however, it depends on the length of the trap arm. The longer the trap arm, the more likely siphonage is to occur at 1/4ipf slope. As for two into one of the same size, the IPC will allow it and even allow the drain to wet vent two entire bath groups without being 2"
     
  15. hj

    hj Moderator & Master Plumber Staff Member

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    Actually, the longer the line is the less likely it is to siphon, because it would take more water to fill it. But, since codes are more concerned with what COULD HAPPEN, rather than what might actually happen, it is still illegal.
     
  16. Tom Sawyer

    Tom Sawyer In the Trades

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    Nope, the longer the trap arm the higher it puts the weir above the inlet.
     
  17. Terry

    Terry Administrator Staff Member

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    Your lavs may be siphoning the p-traps and you may not even know it.
    I know a woman that had a kitchen sink without a p-trap, and she had no idea.
    I was standing over the sink, and it was a putred smell. She had gotten used to it. Just because the builder doesn't understand plumbing doesn't mean it's working correctly. Your builder gave you a line of bull shit. That job would not have passed anywhere in the US.

    And let me just say this. He's used to working with homeowners that do not work in the trades. The Internet is educating those that read. Maybe it's time he takes up reading too.
     
    newowner and MASTERPLUMB777 like this.
  18. hj

    hj Moderator & Master Plumber Staff Member

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    Yes, but siphonage can ONLY occur if the pipe is full of water and the longer pipe is less likely to fill to the point where it would create siphonage.
     
  19. xr4ti

    xr4ti New Member

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    Location:
    Wisconsin
    I have not had a problem with the traps being pulled dry, at least not yet. A friend of mine is currently building a new home with the same builder, same plumber, and plenty of double vanities. I told him to watch for this too. He has a different building inspector, though. The one for my village is outsourced but his city has it's own inspectors, and other local rules, copper water main for one. (Mine is PEX).
     
  20. hj

    hj Moderator & Master Plumber Staff Member

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    "Traps pulled dry" is a "silent problem" that you might not realize until you start getting odors.
     
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