Preston, do you mean a 2" ID thru-hull? I just installed a 1.5" ID thru-hull and had to drill a 2" hole to install it. It also goes into a 1.5" ball valve.
Either way, that will give you access to a lot of water in a hurry. Can you split it into a manifold before reducing it down to 1"? Does the RC III have to work off of just one supply line, or can you feed all 3 pumps separately? It would be a lot faster if you split it 3 ways.