Looks pretty but it stinks. There is some deconstruction involved to get at this one. It can't be helped. The existing tank is GRP and holds only 18 gallons. The hose fittings are bronze and show some signs of leaking. The only way to remove this tank will require cutting some furniture. I had some thoughts on relocating the holding tank but that has passed.
After flushing the system out several times and removing all the old hoses the smell is gone. The pumpout hose remains. It can not be changed without cutting furniture although there is some evidence that a hole was cut in the bulkhead (and patched) to gain access at one time. We cleaned the fittings thoroughly so hose connections will be less likely to leak.
It's alway fun rip stuff out but, it seem like we are doing way too much of this.
We decided to use a freshwater flush toilet. Seawater is full of organic mater and also reacts with urine to produce that 'boat smell'. Seawater is usually used to conserve fresh water. However, since this boat has a water maker we do not need to be as conservative regarding water use.
Also the plumbing was somewhat complicated. Simplifying this will result in fewer hoses (often the source of stink). The toilet can be reversed reducing the hose run to the holding tank thus taking only 6 vs 12 pump strokes to flush.
Because the tank has two discharge ports (the pump out and maserator pump) , there's no need to have a three-way valve to discharge overboard. All blackwater will go directly to the holding tank. A diaphragm pump will be used for overboard discharge (when off shore). Finally, the anti-syphon valves have been relocated closer to the centerline of the boat under the sink.
Of course moving things around means that all the old holes need to be filled in. This takes some time.
So, I finally figured out how to make access to the pumpout hose connection on the tank. I had to cut a new access panel on the settee. After that it was strait forward. There still some issues with the vent hose. It takes a route that goes down from the top of the holding before leading to side of the coach roof. This means that it will always contain some water.