koliver wrote:A hard pipe will be better for a long run, as the soft pipe will sag and allow puddles to form. In a waste line, that can not be good.
No...it's not. Which is why a long run of hose--any hose, not just sanitation hose--should be supported on hangers every few feet to eliminate the sags.
Hard pipe in sanitation systems is really only recommended for long straight runs, and it also needs to be supported every few feet.* It should also be "soft coupled" to anything rigid--toilet, thru-hull, tank, macerator pump etc--with enough hose to provide shock absorption...'cuz PVC becomes brittle enough in very cold weather that even a sharp rap against a dock can crack it.* So unless you have a long straight run, you're gonna have so many pipe-hose and other unions in it that there's really no advantage to hard pipe over permeation resistant hose.
Otoh, if it's not a sailboat and spends 90% of its time at the dock or cruising placid rivers and lakes,* you can get away with hard pipe no matter how convoluted the plumbing runs.* But I wouldn't advise it for boats that do trans ocean passages where it's not unusual to spend a day or longer in 10-15' seas.* I remember hearing from a boatyard owner in south FL who'd just gotten a 60' trawler in that had taken such beating in a storm coming from somewhere in the Caribbean that not only had the pvc piping cracked, but two fiberglass* tanks had as well!