Hi, I am in the construction stage for my reef tank, but before I get anything drilled...

I will be using and external return pump to push water from my sump, back to my display. The pump has a 1" inlet and 1" outlet. My question is in regards to the PVC pipe that runs from the sump to the inlet of the pump. Should I oversize this pipe or keep it at the same diameter as the pump's inlet. I've heard you can have problems with cavitation.. although I 've seen plenty of systems online that appear to have the same diameter pipe as the inlet.

IMO, If you are like me you would want to be able to clean the pump. So i would go with 1.5" so you can place a inline ball valve and a union. So in order from sump to pump you would have, 1.5" pipe,1.5" Ball Valve - 1.5" Union Combo, 1.5"pipe, 1.5" to 1" reducer, and then your pump. That way you can shut the ball valve to turn the water off so you can disconnect the pump..

If i could make one recommendation it would be to have a Rubber maid container under the pump so when you disconnect it you wont get water inside of your stand. You can buy a medium sized cake container at Wally-World and cut it down so the pump and the piping can fit comfortably inside of it.