Lets talk about the tank… please describe the current condition ( pictures would help) , Is it intact? any holes? big holes or rust pin holes? Can you remove the cap? look inside? much rust? From the picture that you have posted it looks like the tank is pretty much intact.
With a better assessment of the condition, we can give you some guidance as to how to proceed.
Also, have you told us where you are located? Local assessment/ help may be near.
Joe B