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Thread: Connect toilet directly over main drain. 3" clearance under subfloor to top of drain.

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  1. #1
    DIY Junior Member zx6e's Avatar
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    Oct 2012

    Default Connect toilet directly over main drain. 3" clearance under subfloor to top of drain.

    I've checked out this site for almost a year here and there and finally joined today. I've searched a lot for an answer to this but the Q is pretty specific. (and more to come no doubt).
    Move toilet 8" or up to 10" into existing bathroom so I can move the wall in the matching needed 8" -10" (to connect my garage to my house, create a new main entrance to house and mudroom etc...)

    Can I tie into my main drain (white PVC) below - I want to go direct in since the main drain is directly under where I want to have the closet flange drain. The main drain is flush up against this 'farthest' floor joist that I want to go to (without relocating drain or chopping huge holes in my small floor joists). I *might* be able to offset the main drain, essentially flip sides of the closet out and wye in that exists right now, and the main drain but it's going to be a lot more work and a little dodgy with some of the other constraints in the plumbing and framing right now. I measured the distance from my main drain uppermost part of the pipe going up to the subfloor and it's about 3". Which seems quite shallow for a combo, or a wye and 1/8 solution. What could I tie in with here? (I know the Sanitee is not ok here). Home is in NH.
    Right now the closet flange has a very short 3" section in a wye on it's side that goes into the side of the main drain.

    My house was a small 1000 sq ft ranch (with full height basement for easy under access), that had a huge garage added to it, with a 6' x 24' connector 'dead space' as I call it. The space connects garage to house and is all framed and roofed but not finished and empty. I want to make new home entrance there, and thereby re-do my kitchen and relocate it somewhat with new island cooktop etc...

    What I need to do it this, move the toilet at least 8" ( I have what I've measured as a 24" wall space now that I want to cram a 32" door into).
    There is the home main vent in that wall which I'll also have to move, the cold water toilet supply, and the closet flange.

    I have 2' x 8' nominal floor joists in the house on 16" center (7" actual). There is already a cut out area around my toilet where the joists were cut and boxed out for one joist, so I've got a 32" box essentially to move things around in.
    If I move the closet flange or toilet out all the way to the far side of that 32" opening right up against the joist, I can move it laterally 8".
    The toilet has standard 12" rough in. I mocked up 3 views of the house on Adobe InDesign with current plumbing and desired plumbing routes I can jpg and upload here if helpful (that was my initial plan - to have those ready for scrutiny).
    I could also switch to a 10" rough in toilet to gain another 2". And what about these toilets that have the rough in all the way at the back? Or a wall mount model?Crazy ideas? (I may need it once I start demolishing my wall for a door - door needs to be minimum 32" width for code legal garage entrance. I have a 36" front home entrance already, and (2) 36" french door openings so I am covered for a full size main door for code there already).

    One bathroom only for whole house. One toilet. Main vent is 3" that is located within 5-6' of toilet.
    Name:  toilet flange nh.jpg
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    So in this attached pic, this is plumbing as it exists right now.
    Vertical line on right is main 3" DWV pipe for house. Current toilet out on left. I want to put the toilet drain directly over it somehow if that's possible. If there's a way, that's going to be the best solution. Can I use a 3" x 3" x 3" spigot closet bend or something like that?
    Last edited by zx6e; 10-31-2012 at 02:16 PM. Reason: attached pic and more info

  2. #2
    DIY Junior Member zx6e's Avatar
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    Oct 2012

    Default Anyone with a suggestion how to do this?

    Here's a diagram of what i am talking about and what I want to do - have the WC directly above the current main drain.
    With only 3" empty space above drain pipe.
    Attached Images Attached Images  

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Aug 2004
    Cave Creek, Arizona


    In its simplest terms, NO. That toilet, because other things will be flowing past it, needs its own vent. How you arrange, or rearrange, the piping to accomdate it depends on factors we cannot see in your pictures. From the pictures, however, what you have now might also be improper.
    Licensed residential and commercial plumber

  4. #4
    Forum Admin, Expert Plumber Terry's Avatar
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    Aug 2004
    Bothell, Washington
    Blog Entries


    A vent will be needed between the toilet and the main line that runs by it.

  5. #5
    DIY Junior Member zx6e's Avatar
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    Oct 2012

    Default Thanks! Here's more info and pics

    Thanks guys! It's nice to have some of the forum heavies weigh in.

    Honestly I kind of confused myself with those posts, and had to get back to my laptop with the InDesign files...
    So including and looking at them now, if you see in the corner of the bathroom, there is a whole house vent there, and I guess it's between the WC and the upstream sinks, so maybe that makes it ok / code compliant? (and up in the attic, looking at the eaves/rafters area I can see the 3" vent pipe and ALSO a small maybe 2" pvc pipe that comes in several feet horizontal on the attic floor into that vent and extends back to the center of the house maybe 2-4 feet - it was hard to tell how far, what it is, where it goes with insulation and bad lighting up there (no finished floor 4.5' ceiling etc...)

    Have two views with existing plumbing as close as I can get it to accurate, and what I think I would like to try to do.
    You can see on the ariel view, where I am looking to cut main entrance, a small future mudroom and off to the offscreen right where the garage is.

    Thanks again guys and love the forum!
    First picture of each pair is EXISTING plumbing.
    second picture of each pair is PLANNED plumbing / idea.
    Attached Images Attached Images     
    Last edited by zx6e; 11-04-2012 at 12:56 PM.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Your drain line can't start down before the vent connection...
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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