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Thread: Back outlet toilet question

  1. #1
    DIY Junior Member alexlacelle's Avatar
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    Default Back outlet toilet question

    Hello,

    I am looking to install a back outlet toilet in my basement. The reason for this is that my waste pipe travels horizontally approximately 5 inches above the slab. My idea is to install a rear discharge toilet with a 45 degree bend turning left and slightly downward to tap into the waste pipe. I need to know whether this would cause me a problem or not.

    I've attached a picture of the waste pipe I'm looking to tap into.


  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    A floor mount back outlet bowl roughs in at 4-1/4" from the finished floor.
    A wall hung bowl can be higher then that.

    Or you can use a pumped bowl, but gravity is the best choice here.

  3. #3
    DIY Junior Member alexlacelle's Avatar
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    Thanks for the quick reply. I'd like to avoid using a pump toilet for noise reasons.

    the 4 1/4 inch rough in is fine. I have no issues building up the floor. Alternatively I found a rear outlet toilet with a 7 inch rough in. Again my main concern here is going from the back outlet pretty much directly into the waste pipe without a vertical drop. I'm concerned about having improper flow issues.

    To help me understand here, could I tap into my existing waste pipe with another y type pipe, a 45 degree on the end of that, with a bit of a downward angle, going to the back outlet?

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    Once the waste exits the toilet, it can only go down or horizontal...it cannot go up at all, and should not go level - the horizontal should have downward slope. If you can make that work, you've got a chance.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    DIY Junior Member alexlacelle's Avatar
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    The horizontal does have a downward slope.

    Will the quick 45 degree turn right after the waste exits the toilet cause me any problem at all?

  6. #6
    Moderator & Master Plumber hj's Avatar
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    It appears that the only thing you have forgotten/omitted is a vent for the toilet, and since it is connected to the waste line BELOW overhead fixtures, it will probably be subjected to "positive" pressures that an air admittance valve cannot relieve.
    Licensed residential and commercial plumber

  7. #7
    DIY Junior Member alexlacelle's Avatar
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    Thanks everyone for the great information. I decided to break up the slab this morning. It went alot better than I thought. This will allow me to put a normal toilet in. Thanks again!

  8. #8
    Forum Admin, Expert Plumber Terry's Avatar
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    Breaking the slab out is the better way to go. I like to hire a sub with a wet saw to cut the concrete. No dust, and clean cuts to pour to.
    Like hj mentions, don't forget the vent for the toilet and other fixtures down there. Sometimes you can drop a vent down from a bathroom upstairs.

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