Catalina 350 International Association

This really feels like it should be a question with a very obvious answer but turning out to not be. I am in the process of redoing some of the potable water plumbing on my boat while it is on the hard for winter and collecting supplies.

I have done a ton of residential plumbing and very comfortable there but first foray into marine plumbing and want to do it correctly so doing my research.

When I look at fittings some say "not suitable for use below the waterline". What does this mean as it relates to plumbing fixtures? Googling seems to suggest that "below the waterline" refers to anything involving a thru-hull which requires a seacock not that the plumbing itself is installed below the waterline of the boat. Is this the generally understood definition?

If the definition is that the fitting is installed below the actual waterline of the boat, most of the factory installed potable water plumbing on my boat would need replacement because a lot of it runs in the bottom of the boat.

Also, my boat is a 2004 and I am 2-hours away and trying to find out the size of the potable water lines (red and blue). I'm getting pretty much an even mix of 15mm and 1/2". I plan to call Catalina but seemed worth asking here also.

Thanks in advance for your time

Please be advised that the new braided tubing from Catalina Direct does not fit the push connectors. I don’t have a source or even know if they had other tubing at CD.

Thanks for the reply Wisail. I plan to transition from the 15mm braided line (if it is indeed 15mm) to 1/2 PEX-A with a barb and I should be off to the races from there for the projects I have in mind. Plan on using either Aqualock or John Guest push connectors (with a slight lean towards John Guest). Anyone have any experience with the JG fittings? Leaning that way because their bypass valve looks to be beefier and they seem to have more variety of fittings. This is all for the water heater and other exposed plumbing so not buried deep in the bowels of the boat. However one is very much physically below the water line which is what promoted my original question.

My 2007 hull 418 is 1/2” line by Sea-Tech. Tougher than nails with blue and red lines. Fittings by same. All are secured by a PEX like clamp.