I've done it a couple of ways. It depends on where your head is located and how the job looks afterward. Personally I don't like putting any holes below the waterline in a boat - it is just a problem waiting to happen. I have bored a hole through the side skin above the water line and welded a tube thru it and down the outside into the water, kinda like a dip tube - this way if it fails it is above water line. On some I have run good quality hose to the transom and put the dip tube there (looks better too I think) and put a check valve inline to keep from losing prime and having to suck a long hose full water before it gets to the head. Just some suggestions.