Offhand I'd say that you are doubling the plumbing system plus you are using a much more corrosive fluid. It would be an interesting experiment, since toilets

Offhand I'd say that you are doubling the plumbing system plus you are using a much more corrosive fluid. It would be an interesting experiment, since toilets use a great deal of water. Take a beach town, build a separate pressure water and sewer system, see if it's worth it. It's certainly more complicated than a sailboat's set up.