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Thread: Double Combination Tee-Wye (Horizontal)

  1. #1
    DIY Junior Member RockRiverShooter's Avatar
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    Default Double Combination Tee-Wye (Horizontal)

    Hello --


    Quick question about adding some additional drain (DWV) lines in my basement floor.


    Currently, I have a 4" CI running horizontally through the center of the basement slab. It runs from one end of the house to the other, where it exits to the outside. The slope is a generous 1/4" per foot and cleanouts are properly spaced.

    I would like to add two powder rooms in the basement which would be located equally perpendicular on either side of the 4". I would prefer to use a Double Long Turn Combination Tee-Wye that I splice into the existing 4". I can then branch out both ways and connect the other fixtures.

    Not asking about venting as this will not be a problem and will be done correctly (separate dry vents to roof line -- not wet vent to vertical stack going upstairs.)


    I figure a regular Double T would not be appropriate, but the Long Turn Combi looked like a good solution. I thought this would be better than splicing in two separate combi's (one for each powder room). I would continue 4" to each powder room as they make the 4X4X4X4 double.


    Any problems with this plan using the Double Long Turn Combination Tee-Wye in a horizontal position? I would prefer this over using two single Combination Tee-Wye's. I know a standard Double Sanitary Tee would be a no-no as it would not route the waste downstream as efficiently as the Double Long Turn Combination Tee-Wye.


    Appreciate the feedback.






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  2. #2
    Moderator & Master Plumber hj's Avatar
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    The sanitary cross is just two sanitary tees, which means it cannot be used in a horizontal drain line. The double combo is the proper fitting.
    Licensed residential and commercial plumber

  3. #3
    DIY Junior Member RockRiverShooter's Avatar
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    Thanks for the quick reply. I added the image of the Sanitary Cross fitting on the bottom as a comparison. It's apparent the sweep is much less on that fitting and I can imagine a snake ( as well as waste flow) would have a much more difficult time going in the right direction in a horizontal application.

    I'll go with the first image of the double combination. This will allow me to branch out in both directions perpendicular to the horizontal main going through the floor.

    Take care!!

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    Forum Admin, Expert Plumber Terry's Avatar
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    The double fixture fitting can't be used on the horizontal.

    On the vertical, the new toilets tend to skip across that fitting, so while it had been a good fitting for the old toilets that took forever to clear a bowl, the new toilets with 3" flush valves don't work well. Or I should say, to overly well and skip across the fitting. If it were my home, I would stack a wye below and make sure the waste from the other bathroom was forced downward.

    Here is a nice link to Bert Polk's plumbing tips
    Last edited by Terry; 07-09-2013 at 06:25 PM.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    quote; The double fixture fitting can't be used on the horizontal.

    It is NOT a back to back fixture fitting. It is a double combo and I used them in horizontal runs all the time. ( I did have a space issue once and the inspector did let me use the fixture fitting.
    Licensed residential and commercial plumber

  6. #6
    DIY Junior Member RockRiverShooter's Avatar
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    Quote Originally Posted by hj View Post
    quote; The double fixture fitting can't be used on the horizontal.

    It is NOT a back to back fixture fitting. It is a double combo and I used them in horizontal runs all the time. ( I did have a space issue once and the inspector did let me use the fixture fitting.

    I knew that a cross or back to back would not be appropriate for the reason Terry explained. Just looking at the fitting on its back, it is obvious there could be a possibility of skipping across the fitting.


    The Double Combination has the long radius sweeps that look like they would direct waste in the proper direction as well as a snake (if ever necessary).

    Unfortunately, was having a bit of trouble locating the Double Combination at my local supply houses in stock. Keller's set me up with a Double Wye and two 1/8's (or street 45's) which is almost exactly the same. I'm happy with the setup and I'm going to give it a try. It's full 4" all the way, so I should be a good shape.

    My trench is a little too tight to stack two single Combinations so the double should do the trick! Proof's in the pudding and sounds like HJ has used this type of setup before with success.


    Take care everyone and thanks for the help!!

  7. #7
    Forum Admin, Expert Plumber Terry's Avatar
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    Plumbing inspectors don't like it used on the horizontal here in Washington State. Go ahead and pull a permit and try them.

    I'm not surprised that hj plumbs that way in Arizona. (And had to get the inspectors permission)

    My jobs pass with flying colors. Besides, it's not about doing the least you can get away with. It's about doing it right.

    Here is a nice link to Bert Polk's plumbing tips
    Last edited by Terry; 07-09-2013 at 06:24 PM.

  8. #8
    Moderator & Master Plumber hj's Avatar
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    The inspector's "permission" was for an individual job and the fitting was NOT the exact one since it was a back to back fixture fitting and NOT a double combo. But otherwise, I have use double combos in horizontal lines for over 60 years, in Chicago which is one of the strictest codes in the country and AZ.
    Licensed residential and commercial plumber

  9. #9
    DIY Junior Member RockRiverShooter's Avatar
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    Hi HJ --

    Finished up the DWV rough in and the Double Wye worked great. I removed a section of the 4" CI and inserted the new ABS fitting. New 4" branches go out in both directions with generous 1/4" slope. I even canted the street 45's up a bit.

    The existing 4" CI was actually in good shape and had a nice slope out to the street.

    Thanks again for the advice/encouragement. I think this will work out great!!


    -- It better, as I just finished the concrete patch work yesterday afternoon!!!


    Thanks Terry Love Forums!

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    DIY Junior Member SupermanSC's Avatar
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    Would you happen to have a part number for the Double Long Turn Combination Tee-Wye in 3"? It's exactly what I'm looking for but can't find one locally, nor can I find it on any manufacturer sites. I don't have enough room for two wye's. This is for a horizontal run.

  11. #11
    DIY Senior Member asktom's Avatar
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    Use a double wye (easier to find) and an 1/8 bend on each branch.

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    In the Trades Tom Sawyer's Avatar
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    I prefer a double wye and 1/8 bend but I can't find anything in the IPC or the UPC that says you can't install a
    couble combo on the horizontal. Its certainly not the preferred method if only because rodding the drain can
    be tricky but hey, thats someone else's problem LOL
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  13. #13
    DIY Senior Member asktom's Avatar
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    I can't see how a double wye & 1/8 would be any harder to snake than a combination, nor do I see anything wrong with using a double wye on the horizonal.

  14. #14
    Moderator & Master Plumber hj's Avatar
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    There is nothing "tricky" about snaking a single or even a double combo. Sanitary crosses, however, are a different animal, no matter where they are installed.
    Licensed residential and commercial plumber

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