That is the main thing I have learned in this forum since I joined last year, that exclusion is the only real solution.

Lundy, is galvanized stove pipe the same thing as the 6 and 8 inch heating pipe in my basement? It has a seam running length wise.

Would you use 5 inch stove pipe or 4 inch PVC for southern flying squirrels? Or would either be ok?

As long as the end is vertical, size won't matter. PVC would work too. Yes, the stove pipe is the same. You do have to push the seam together. I put the seam up. I also add a pole barn screw on top to hold them together. I can reuse the stove pipe for at least one season. PVC would have to be glued to hold together. A lot of my answers are for WCO's instead of a homeowner but they are a different idea than most use.