How can I cut this recessed PVC pipe?
When I had to do this for our basement I used an &quot;Inside Pipe Cutter&quot;, a fancy bit that fits into your standard drill. Looks something like this:
You chuck it in your drill, put the blade at the height you want on the interior of the pipe, and run the drill, cutting through the sidewalls. Won't be 100% perfectly straight unless you have a very steady hand, but for this application it doesn't need to be perfect.  There are versions that have a large disk that rides along the top of your pipe to make straighter cuts, if you really think you need it. I chose the style depicted since it's commonly available at Big Blue and Big Orange
If you need to cut off more of the pipe than this tool reaches, do it in multiple passes.