Columbia 29 fresh water holding tank composition.

[jlchristophel]

Hello, I have a 1963 Columbia 29 Defender. It is requiring quite a bit of work. And now I found that the fresh water tank under the vbirth has been full of water for about 8 years.
Has anyone ever dug into these tanks. How were they made and what were they made of. Through the access port and around the fill cap witch is brass, I poked with a screwdriver and it seems as though the top of it is made of WOOD. Could this be true, all wood holding tank, or is it lined in fiberglass.
I am trying to make a decision about replacing the tank with plastic which would require me to rip out the vbirth. If it is indeed wood I will need to replace the tank, but if it is fiberglass lined wood then I could endeaver to clean it, shok it, flush it etc...

Please help to answer this...
Jesse