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My basement shop toilet was installed years ago (30+?) on a raised wooden platform that rotted out. I removed the toilet, the rusted out metal flange and the moldy, wood platform (2x2 fastened to concrete with plywood on top). I want to reinstall the toilet, but the top of the existing flanged sewer pipe is 2.5” above the concrete floor. It looks like they added a coupling and a flanged ring to the black angled sewer line (but i’m no plumber!).

shop toilet sewer line

I’m considering a couple of options - welcome thoughts and advice. Seems like I have to do either concrete or wood build up to flange height because the sewer pipe begins to curve immediately at concrete floor level. That right? Do I need a coupling to the existing set up to raise it further so I can insert a new flange and have a floor to attach it?

current flange height

I don’t know if I need the existing flange on the pipe now. Cut it off or leave it?

Once I build up the floor/platform, can I use one of those Oatey twist and set replacement flanges and just set it on top of the existing flange. Glue it down? It’s a 4” opening but I don’t know how deep it needs to be for the inserted fitment to work properly as the pipe begins to angle quickly.

sewer pipe opening

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An Oatey Twist-n-Set won't work for you, unless you raise the floor even more. The part has an almost 3.5" depth, requiring the receiving pipe to be straight for at least that depth. It looks like your "coupling" is only an inch tall. I'd recommend removing the coupling and seeing what you have left, and trying to mate a new flange to that.

As to the floor, I think you're stuck raising it with (PT) wood again. What I'd probably do, though, is to build a concrete base to the level of your new flange, just a box in the footprint of your toilet—the wood sub floor would go around this.

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