If you are putting a tub in that would easily fit on the space at the bottom of most tubs. If a shower you could attach 1 1/2 strips of wood or metal to the studs but then you might want to move your drain.

Bust pipe out with sledge hammer, cut offending part off with sazz-all, trim around pipe and paint expose part a pretty color then put knuckle knots on the plumber's head.

" Interesting preslope . "

"Interesting" being the operative word...................

If that is a shower you need to do some more demo and considerable more prep work.

Yeah, I had a similar issue. They put a cast iron main stack inside a 2x4 wall which was the back wall of the tub. The hubs on the pipe joints stuck outside the plaster and were right behind the tile. Not really sure why it wasn't waterproof.

I had to furr it out - which really messed with everything such as supply and drain lines, as you might imagine.

You have to love those little surprises!

Please clarify? Are you putting in a new tub since the plumbing is showing that? If so then that bump will be behind the tub. The tile doesn't go all the way back there.

If it is becoming a shower, then just fir out a 2" bump over it or fir out the whole wall to cover it.

"... then just fir out a 2" bump over it or fir out the whole wall to cover it..."

The tub spout, etc. is from the previous tub. It looks like he intended to install a shower. Furring out the wall will require moving the drain and some of the supply to keep it centered.

At this point I'd possibly re-think the shower.

The waste stack bends like that to clear the footing ledge. The cleanout would need to remain accessible.

If there will be a tub (because of the spout), the drain will need to be demo'd and a large rough-in opening left for alignment of the Ptrap.

The old corner shower pan appears to have sat in gobs of thinset to level or support it. It isn't presloped for a prefab pan.

If you install a mud pan (which would be hand sloped), the location of drain and mixing valve is not as critical, it can be placed dimensionally on any criteria. If it is another prefab pan, then the drain location will matter if you furr out the wall.

Batt insulation against basement concrete walls, and any air spaces, allows the risk of condensation, which allows the risk of mold behind the wall. The wood stud, and possibly the drywall fireblocking, might be showing some of that.

@3onthetree

You raised some good points:

It wasn't clear to me what was going on there - my thought was that there was a tub there previously and he's going back with a corner shower.

Now that you explain what pattern is, it makes sense. A shower base was placed on top of a mortar bed. I don't know if that was old, or he placed and then pulled it up when he discovered the main stack was in the way.

You are right that the drain isn't quite so important if it's a custom pan - but it really needs to be centered or otherwise make sense. You don't want to finish this big project and then be looking at a randomly placed drain. It would make me mad every time I saw it.

I saw the cleanout issue - but I don't know what you do about that at this point other than plan on an outside cleanout. Most sewer cleaning companies don't want to haul their machines into your basement anyway - they want an outside cleanout. I'm sure that's partially driven by revenue opportunities also. For some reason that cleanout faces to the side and there are studs in the way. I think the cleanout access ship sailed a long time ago.

I also saw the wood and fiberglass - and that's a big "nope" for me too. It's built with steel studs -- why would someone put wood in there where it will rot and be a path for termites? But I also have the impression that's the way the rest of the basement was finished. That said, I understand the idea of "make your work right, even if the rest isn't"

Look OP, I don't think it matters if you are doing a custom pan, a pre-made pan, or a tub. You are probably going to relocate that drain (my guess is that you did that once already). If it's a shower you will bump that wall out.