Bev, On the PVC, I wet sand from 220 to 600 grit then Beall buff...that's it. When buffing, you'll have to load up the Tripoli wheel and crank up the speed to get the tiny scratches out.
Dog, the PVC I'm using is called "PVC Type I extruded rod". It does not shrink. That's all I know about it. If you get some lazer'd, let us know how it turns out.