My 2006 C Dory 22 had a live well, with a Built in floor input and an overboard drain, which looked to be factory done. This was in the Port Lazarette. I have seen several others which were similar, and had a vane type of bait tank pump between the thru hull (scoop type) and the input to the tank.
I don't remember the fitting size. I believe the pump was the Rule 401 STC--but not sure--if so the hose was probably 3/4" from the pump to the input. The foot screwed into the thru hull, or a union. with 3/4" or 1/2" American Standard pipe thread (plastic).
I would wait until the boat is in your hands before you purchase fittings. Most likely a nearby West Marine or even Home Depot will have all which you need. For the C Dory plastic (or nylon) fittings will probably be fine. Bronze (not brass) would be the best. If the boat was plumbed for a bait tank, there will probably already be a thru hull. If there isn't--then the problem becomes far more complicated as Paul notes: there is a cored bottom, which needs to have the proper size hole drilled, the core undercut, filled with thickened epoxy, and then smoothed to take the thru hull fitting. The scoop, needs to be in a position which does not interfer the the trailer or give turbulence to cause ventilation of the prop.
