I use clear tubing from my overflows to my sump and use PVC
to go from my return pump to my tank. You can use PVC
both ways if you wish. I like the tubing for my drain lines as it permits me to mvoe the drain lines if I want to.
If you use PVC
you should invest in some true unions and some ball valves. The unions will alow you to disconnect the pump from the rigid plumbing with out having to cut the pipe. You would also put the unions just below where the plumbing connects to your tank (if your tanks 'reef ready'). This way you can disconnect your plumbing from the tank when/if you move the tank. Else you will have to take a hacksaw to it and cut the plumbing off and then deal with refiting the plumbing later.
The ball valves will allow you to cut the water off when servicing the sump, pump or plumbing. I would put ball valves directly above the true union thats above the pump so you can turn off the water from the return lines and then remove the pump with out dumping alot of water. The ball valves above the unions on the tank return would permit you to cut off the water and then disconnect the bulk of the sump's plumbing for repair/replace with out having to drop th ewater level in the tank to a point where its below the return lines.