Rigid PVC ok for long straight runs, but...
...not if you'll have to insert a bunch of unions, bends and elbows...they become traps for bits of solids and paper, and the odds of a clog goes way up. And, you'll have to use enough hose at the toilet, tank, macerator, y-valve, through-hull--ANYthing else that's rigid--to "soft couple"...iow, act as a shock absorber...so although rigid PVD doesn't permeate, you may not gain much. With the exception of the new (5-6 years now) SeaLand "OdorSafe" hose, no hose is gonna last more than a few years without permeating. The biggest reason the head discharge hose permeates is because most people stop pumping--or take their finger off the button--as soon as the bowl is empty...and when you stop flushing, whatever is in the system stops moving...so the hose stays full of sewage that's only being moved along a couple of feet each time the toilet is used. On any tank on which the discharge fitting is at the bottom, the tank discharge hose is always gonna be full of sewage to the level in the tank...so it's gonna permeate (and it's one of the main reasons why we like to put all the fittings in the top of the tank, with a tube inside the tank to the bottom on the pumpout fitting). VacuFlush toilets create the most hose permeation problems (and why SeaLand had no choice but to develp a "bullet proof" hose): the suction when the vacuum is released splatters waste all over the inside of the hose and the vacuum tank...and the water flow is too light to fill up the hose and rinse it out. If you want to extend the life of your hoses, it's absolutely necessary to flush enough clean fresh water through the system every day--and especially before closing up the boat at the end of a weekend--to completely rinse out the system. A cup of white vinegar down the toilet afterward is recommended to dissolve the urine crystals and sea water calcium carbonates before they can harden...I've seen those reduce a 1.5" ID hose to less than 1/2" in a year if the boat is used a lot. With VacuFlush, once each day, fill up the bowl completely with water twice and flush that through. I rehosed my own boat with the SeaLand "OdorSafe" last fall...at $8+/ft, it's expensive...but in the 5-6 years it's been on the market I have yet to hear of a single case of odor permeation failure. So which costs more--$8/ft once...or $-3.50-$4.50/ft every 3-4 years?
