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Our boats freshwater system still had the 37-year-old OEM hoses when we bought her. The hoses were dark and gummy, not something I wanted to even wash dishes with, let alone teeth. The freshwater pump would not stay off unless I flipped the breaker, so we decided to update the plumbing. Initially I was going to replace the hoses with new ones, but they were pricy and I needed a fair amount.
When we were looking for a boat, a lot of the newer ones had PEX pipes in them, so I looked at that. The price was good, so I bought a jar of cinch clips, a pinch clamp tool, fittings (Ts, 90-degree angels, a ball valve and a backflow preventer) and some red and blue PEX-B pipe. The push to connect (Shark-Bite) fittings were expensive, so only the backflow preventer is that type. For the water heater, pump and sink connections I used swivel connectors so I could remove them if needed without having to cut them off. I made some sub-assemblies for the areas too small to get the tool into and connected them to the rest of the system.
NOTE: PEX-A and PEX-B are not the same and use different fittings and tools. I recommend PEX-B for a boat.
The system is now updated, clean and best of all watertight. The freshwater pump only comes on now when I use the faucets.
(See article on adding a Freshwater Pressure Reducing Inlet.)