If you want an odor-free head installation on a boat, high-quality hose is extremely important. I went with the Trident #102 rubber sanitation hose. Although it's around $10/foot, that's well worth it for making the boat more liveable. And it's much more flexible and durable than the older PVC reinforced #140, making installation easier.
But even this hose is not flexible enough for the tight turns needed to tuck the plumbing away out of sight. I looked at Mike Lehman's installation on Gilleleje and, while he hasn't had any problems, I was amazed at the number of hose clamps. Each sharp bend required an elbow and two hose clamps. And the hose-to-hose elbows are sharp bends, indeed. And so, I decided to use PVC pipe.
Now, PVC pipe is not generally recommended for a boat. Because it is rigid, it will crack as the boat flexes. But I reasoned that if I let the pipe float free, mounted only by the hose connections, I wouldn't suffer any such problems. Time will tell, but the first year looks encouraging.
I assembled a collection of 90 degree street elbows, a sanitary tee, female adapters, hose barbs, and pipe all in 1-1/2" size. I made up the assemblies shown, dry-fitted, and then cemented them in situ.
The U-shaped assembly connects the head outlet to the holding tank inlet. The Y-shaped assembly connects the holding tank outlet to both the deck pump-out fitting and a Jabsco macerator pump for overboard discharge when offshore or in emergencies. You can see that the deck pumpout is aligned over the existing holes in the shelves where the anti-siphon loop was originally installed.
The macerator is mounted inside the lower head locker, bolted to the shelf of the upper locker. There is not Y-valve. As long as the hose fittings are air-tight (and they'd better be, anyway) and the through-hull is closed, there is no problem pumping out via the deck fitting. The sanitary Y gives a gentle sweeping curve in that direction to avoid restrictions.
Installation is completed with a 1" connection to the existing through-hull. A 90-degree hose coupling is used to turn the corner from the macerator outlet.
At the through-hull, I used a reducing coupling to match the existing plumbing. A plastic wire-tie, screwed to the bulkhead, legally locks the seacock handle for inshore sailing.
Special thanks to Mike Lehman of Gilleleje, #505, and Jim Mennucci of Quest, #433, who blazed the trail with the Kracor tank.