Tips for tight-space toilet drains that nobody talks about

I just finished a basement remodel where I had to tuck the drain into an 8-inch soffit, and using that street 90 into the wye was exactly how I handled the drop. I used Charlotte Pipe PVC and some Oatey Purple Primer to make sure everything was bonded tight. One thing I ran into was the 4-inch stack transition; I actually opted for a 4x4x3 sanitary tee instead of a reducer because I was worried about the sweep radius in such a cramped spot.

The 1/4 inch per foot slope is easy on paper, but once you're holding a heavy assembly over your head while trying to avoid the HVAC ducting, it gets tricky. I found that using plastic strapping to pre-set the height helped keep the pitch steady before I did the final solvent weld. Like you said, once that glue sets, you're stuck. I double-checked the deburring with a pocket knife because I've had hair and debris snag on those internal lips before, and that’s a nightmare to snake out of a finished soffit.

I had a similar headache with a 3-inch run last summer. The plastic strapping is okay, but I switched to using those adjustable metal riser clamps to lock the pipe in place while I was solo. It stopped the pipe from bouncing around while I was trying to shove the street 90 into the wye. Also, I started using the heavy-duty gray cement instead of the clear stuff for these overhead joints. It's got a bit more body to it and fills the gaps better if your cut isn't perfectly square. Saved me from a slow drip that woud've ruined my drywall.

I've started using a battery-powered deburring tool for those tight spots. It's way faster than a pocket knife and gets the inside of the 3-inch pipe smooth as glass so nothing catches later. Also, don't forget to mark your alignment on the dry fit with a Sharpie. When you're wrestling with that glue in a dark soffit, it's way too easy to end up a few degrees off and mess up your whole pitch.