I have a 30 gal fiberglass water
tank on my boat that has some black material on the bottom. Tried bleach added to water. Got some but not all. The small opening on top of tank makes it very difficult to get any type of stick or whatever, in the tank to wipe clean. However, there is also a large round (lid) that has the hoses going thru it. It seems to be bolted to the top of tank. Can the large lid be removed without hurting anything? U
As always, thanks for your input.