Sheesh, I don't know. I've never done that, and it's something I'd think about for awhile before I committed. Maybe Waste or Waterbear has done something like that, successfully.

Off the top of my head, I'd probably go 3", so I could fully pack cement around the stub-out. If you get too snug, it's going to be really hard to fully pack the annular space around the pipe. I'd also be inclined to put a coupling halfway between the pool side and the dirt side of the shell, as a waterstop. But again, I've never done it before.