I believe he had a lot of water in the boat at one time during a heavy
rain storm. It's an older boat. He had a lot of posts trying to get
it running after that. It was in a slip at the time so siphoning the
water may not be an option.

I suspect that the water level got above the top of the tank and it
leaked in then. After 20+ years the gaskets around the sending units
are not in the best of shape. It normally doesn't matter because they
are at the top of the fuel tank.

Keith wrote:
When you don't keep your tank full, moisture condenses inside on the
cool tank sides as the atmosphere heats up and cools down. Your tank
"breathes" through the vent. That's one way, at least. Check to make
sure your vent isn't turned upward where it can catch rain. I bought a
Cruisers, Inc. boat that came from the factory that way! If you can't
find obvious leaks, just keep the tank full and that will probably
solve your problem.