This is the forward "V" berth. Lovely teak. Storage bins all around. Under the cushions is one of our water tanks. This is where it gets scary. Cindy Ann busted out the pry bars and putty knives and—slowly, patiently—ripped the lid off the water tank, hacking away 30-year old gasket material. This scares the willies out of me: "How will we ever get this back together again?"
Worse, of course, is the "what will we find?" question. What condition is the tank? Is it filled with decades-old biology experiments gone awry?
Do we really want to know what's in there?
We do know that it leaks. I filled it. Months later, we tried to use it for fresh water and found that it was empty.
There's no doubt that it needs to be fixed. The Commodore is absolutely correct, the top needs to be torn off and we need to figure out what's wrong.
To our great joy we found that the inside of the tank was almost pristine. Very, very clean.
What we observed was (1) about a cupful of water at the bottom and (2) a water line part way up the side, (3) nuggets of what is probably aluminum chloride. We think the upper water line is an indicator of a larger pinhole leak on the welded seams. Water drained down to that level quickly and then sat there for a while. The lower level of water is a smaller leak that the water eventually drained down to.
Cindy Ann cleaned the inside by swabbing it with vinegar water. No soap or chlorine. Soap is difficult to rinse out. Chlorine attacks aluminum and leads to small, white chunks of aluminum chloride crystals in the tank. These can clog the pump; and it indicates damage to the tank seams.
The repair appears to be Silicones Unlimited 5005 food-grade silicone sealant along the welded seams. Or perhaps Perfecto Aquarium Silicone. The alternative is to cut the entire top off and insert several smaller polyethylene water tanks into the the space.
Some folks suggest say we should never add chlorine to the tanks. Some folks say never use municipal water without a chlorine filter.
Perhaps we should get ourselves a home water filtration system and use it for all water that goes into the tanks. We'd put a dock-side hose fitting on one end and a short hose into the water tank on the other end.