We used to have a Class C that we bought used. Someone had put a hole in one of the bottom corners of the water heater flange. It was just big enough for a piece of pipe to fit thru it. So we screwed a few PVC fittings, shut off valve and piped it down to under the RV. To be honest, I really don't know why they don't come from the factory like that. But then there's a lot of things on RVs that I wonder about.