I bought a Whitby 42 last June and she has water, fuel and dirt in the
center fuel tank. This tank is located in the keel with an access
plate almost under the motor. I sucked out everything that I could
but the tank is fare from usable.

Anyone have any suggestions how to clean up and seal off this tank so
I can use it?

Steam cleaning works well if there is someone with the equipment to steam clean
around you.

Dick