Thanks everyone. I used the Unions on both intake and pressure sides. However I now have a small leak/drip where the 2" threaded PVC pipe goes into the pump discharge port.

The Pentair instructions say do NOT use teflon tape, so I used only teflon pipe dope on the threads. When I removed the fittings from the old pump it looked like the installer used only a clear rubber-like "silicone sealer" (like used on a car's valve cover gasket) on the threads of the PVC pipe - no signs of teflon tape/dope.

What do you guys use?

Thankfully I installed the Unions (instead of gluing a coupler in) so I can easily remove this piece of pipe and reseal.