Is this an underground storage tank or ...?

Hello, I am in the process of buying a home. The current owner says that this is not an underground storage tank but it is a clean out for the old wood stove that the house used to have. It goes down about 3-4 feet and has a chimney like structure that is comes out of the ground. The inspector I had said that it could be an underground storage tank for something like fuel oil. I will attach photos and any help would be greatly appreciated.

A cleanout for the chimney would make sense (and match tools that are inside).

Now that is interesting.  I don't know for sure what it is.  But I doubt it was for fuel oil.  The chimney between the hole in the ground and the house is likely connected to that passageway between the bottom of the hole and the basement.  Oil tanks would likely be better sealed (not a plywood top) and would have a smaller pipe going into the building.  Even if that wasn't rusty, it wouldn't hold oil very well.  

I'd be tempted to believe that is was a curious clean-out for a wood stove.  Or maybe part of a still?  Or a charcoal retort?  Or a way to cook a pig with the wood stove?