This was a major job, and took three days, + or -. First I cleared the V-berth area and unscrewed the wood cover over the vent hose and wiring on the starboard side. Then, I went to the pump-out station. I followed the pump-out with two thorough water rinsings. I emptied and removed the head, placing it over the holding tank for storage. I removed the hose from the head to the holding tank and the vent hose. I removed the hose/fittings from the holding tank and the y-valve. One hose went from the y-valve to the deck fitting. Removal was two-steps, First, I cut the old flex hose (original equipment - 18 years) off about 10 inches below the fitting, then removed the hose. The deck fitting had three screws, then pried-off with a screwdriver. Finally, from the y-valve through the macerator, vented loop, and to the through hull under the sink were all removed and disposed of. All the chases and bilges were then thoroughly cleaned with a bleach and simple green solution. Our rebuild strategy was to use as much PVC as practical, connected to the fixtures with Trident 1 1/2" sanitation hose. Trident black rubber hose is much easier to use than the white hose, as you don't need to soften it up. It easily slips over 1 1/2" fittings. As it turns out, 1 1/4" schedule 30 adapts well to 1 1/2" hose. But, before you try this, check-out the fittings you propose to use! We ran a piece of 1 1/4" schedule 30 PVC up under the holding tank, then through the chase. A friend had some schedule 40 PVC cut into 12" segments and 4" of one end turned down to 1 1/2". These substituted for many threaded fittings, and were easy to use and cut with a PVC pipe cutter. One of these was used to prepare a pipe end for Trident to run to the head. These pieces of PVC were also used for the other two pipes that had to fit in the chase between the area under the v berth and the area adjacent to the space under the sink. Using 90 degree elbows, a couple other pieces of PVC, and a piece of Trident, we made the connection to the holding tank. The vent hose was one piece of 3/4" flexible water hose, all the way from the tank to the through hull. From the holding tank, pieces of Trident and elbows lead to the y-valve. Next day. From the y, one leg goes via Trident, a 45 to PVC, a 90 elbow, up towards the deck plate. I used a spiral saw on a Dremel to enlarge the hole through which the Trident must fit through. We reseated the deck fitting and brought the Trident up to it - finishing one leg from the Y. The other leg was similar through the chase, a 90, a short PVC rise, another 90 to a piece of Trident, another 90 to a Guzzler 500 pump, mounted on the back wall of the cabinet using 1/4"ss bolts, lock washers and nuts. Be careful of placement - we removed the sink and replaced it several times as we placed new hose and the pump. Also, assure clearance so the door under the sink will close, and you can operate the pump. The pump I bought has a horizontal handle. The next hose went from the pump outlet back through the space adjacent to the sink behind the wall to the vented U, through the U, back down through the chase behind the wall to the through hull. The shelf adjacent to the U had to be cut away to get the vent and Trident to fit. We discovered the U is not a 180 degree U, but spread out at the ends, requiring this shelf cutting. AS you get into this job, you'll appreciate that this is very tight quarters. A piece of Trient was fit to extend from the end of the holding tank pipe to the fitting on the head, which was replaced in it's original place. Now, to empty the holding tank offshore, I'll use the guzzler and should have the tank empty within 2 minutes, and not have to be concerned abou the electric macerator. Everything fit back together and no more head smell. Thanks to all who gave advice. It's a hard job and requires patience and lots of holding your mouth the right way in small places!