I would give a quick read through the instructions. I set that up recently for my 90 gallon upgrade (using the megaflow kit).
I believe the return was 3/4" ID and the one going from the tank to the sump was 1 1/4" ID.
Go to a fish store to buy the tubing. Most sell it by the foot. HD will charge you 20 bucks for 10 feet of hose when you only need 2 maybe 3 feet.