Till the SeaLand hose came along,
most sanitation hose permeated within 3-5 years...in extreme cases in which sewage was left to "ferment" in the hose, in a matter of weeks (my own did in less than 2 months). All hose is water-absorbent to some degree...the thicker the hose, the tighter the molecules, the more water resistant it is--which is why the softer easer to bend it, is the faster it tends to fail. It was believed until recently that double-walled rubber hose was the most water resistant, but Practical Sailor tests showed that black rubber hose sanitation hose permeates even faster than top quality white flexible PVC hose. Rubber industrial grade or exhaust hose is even more water/odor absorbent than that. SeaLand solved the problem by encasing hose in a "skin" of material that's virtually 100% impermeable. Rigid PVC--hard pipe--is 100% water and odor impermeable...but it doesn't bend at all, requiring inline fittings to go where even the stiffest hose would bend easily enough to make it with no problems. And, because it doesn't flex or bend much, it's necessary to "soft couple" hard pipe to any rigid object--tank, pump, toilet, through-hull--with about a foot of hose that acts as a shock absorber. Otherwise, heavy seas, or even a sharp rap against the dock could crack the hose or whatever it's attached to, whichever is weaker. That doesn't mean you can't use it...it just gives hard pipe very limited application: long straight runs are the only places it should be used. Trying to use it throughout, with bends and elbows at every turn creates bumps, nooks and crannies that trap solids and paper and can lead to clogs. So when you consider all that's involved, coupled with the need to use some hose anyway, most people don't think it's worth the gain to use just a few pieces of it.