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photo of the Long sweep combo fitting with the 45 degree toilet flangediagram of planned DWV layoutPlease bear with me, as I am no plumber, beyond being able to sweat copper pipe, and glue PVC successfully. Thanks, in advance, for any help you can offer!

Here's the simplest version of my question:

Can I safely use a combination of 45 degree Closet Flange with a 45 degree tilted 3" Combo Wye into my 3" drain line? It will fit, but will it function suitably?

I am in the process of turning a shed into a house for our eldest's little family, and need help with a waste drain dilemma. The timing of weather, money, delivery, and site prep delays put us in the position of now having the shed on a packed gravel base, with no added elevation. Skids on the ground, joists across those skids, leaving little room to fit waste drainage.

I have the water in, and distribution figured, and the venting mostly lined out, but the exit portion of the process is daunting. I know where I need the drains, under the current layout, which was set up to keep it all draining out under the south side of the building, between that outermost skid and the actual outer wall - all in one line, flowing out the west end of the building's skirtline. The space is so tight! (8-10 inches!) Besides the difficulty of managing to fit the main line under the rim of the building, let alone get it up to the proper position to accept the drain/vent fittings, and maintain a minimum of slant, is the water closet position.*

-IF- I can use a 3" longsweep combo fitting, turned 45 degrees to the inside, and a 45 degree closet flange, I believe I can make it work. Can that be used safely? The entire drainage line will be 3" PVC, with Kitchen sink, Dishwasher, Lav, WC and Tub/Shower, in that order, top to bottom, East to West.

I know I may have to tear up some floor decking if the line-up is quirky, but I want to avoid that if possible.

*NOTE: I have to plumb for the toilet drain now, even though we won't be utilizing it until the septic receptacle is installed at a much later date. Can't get the thing insulated until all the in-the-wall stuff is complete. Can't skirt till the drain is completed, and can't put the new siding up until the rest is done. Using a composting toilet til then, and grey water drainage as well, directed away from the building.

Thanks for your time and thought!

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    Can you show a drawing or plans? Will this be inspected and will a permit be required?
    – JACK
    Aug 28 at 15:05
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    Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
    – Community Bot
    Aug 28 at 15:05
  • Yes, can you get us photos or a diagram of your situation? Aug 28 at 15:20
  • Where are the coldest winter temperatures you will see, that will have a big impact on what you are trying to do.
    – Gil
    Aug 28 at 18:35
  • Hi Gil, thanks for you question. We typically see temps down into the 20s to high teens most winters. I am planning on adding heat tape along the length at least until the final route to the future septic system is in, as well as a solid 1 1/2 foamboard layer behind the skirting between the DWV and the outer wall.
    – anniemcu
    Aug 28 at 23:03

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