While winterizing in the late fall, I noticed that the seal on the top of the holding tank finally decided to go. Not catastrophic, still holding water in the bilge, but bubbles coming up when pumping the head. That and some nastiness in the water tanks prompted my big winter project, now nearing completion: re-plumb all water systems, and replace those wobbly old thru-hulls and seacocks while we're at it. For the blackwater system I opted to put a 25 gallon polyethylene tank under the "L" of the port settee, just forward of the galley sink. Ronco Plastics makes one that I swear was designed just for this area - fits perfectly with a bit of modification to the box. This had the added advantage of working perfectly with the existing hose routing. No need for new deck opening or vent, can simply bypass the old tank fittings. For freshwater I used that snazzy color coded PEX stuff with the quick connect fittings - couldn't be easier. (Pics below were taken before I got to this part) The last piece of this particular puzzle will be adding a deck wash up by the anchor, and plumbing both head and deck wash to be able to use either fresh or salt water. This will be a bit tricky given the various materials and hose sizes. If anyone has done something similar I'd appreciate any advice you might have.