This responds to an oooooold posting that I'm inexplicably locked out of, so can't respond there. I originally had a porta-potti with pump-out and vent. I plumbed in a 20 gal plastic tank in the first locker under the v-berth and have never regretted it. I did as much plumbing as possible with residential PVC drain pipes. The marina pump-out is easy and when I go 3km offshore I can hand-pump the tank.