Refinishing fiberglass water tanks?

[OloteleMtn]

My tanks on the 40 year old boat i bought were full of grungy stuff, and it seems like i need to sand and recoat the tanks with something. It would be good to have potable water from the tanks; what can i use to recoat and seal the inside?

[Reefmagnet]

There's coatings made specifically for that application. Look for stuff used to seal the water tanks used to catch rain water.