I used to run a service station many years ago. We had leaky tanks and the owner had to replace. The problem is not that the oil eats the metal. The problem you face is how it was installed. The hole where it was installed has to be prepared properly. That includes something similar to a septic tank. A larger hole than needed, bottom full of gravel, then lined with sand. This is to drain the water from around it so it's not holding water to rust. Hard to tell how it was installed.
To pump it dry and remove it, will not be an easy task. You run the risk of it crumbling when you lift it out. If by some chance it is in good shape, and the contents is pure oil, then you have many options that has been discussed here already.
As far as using it to heat with, here's another option. Fishunt on this board, dad, used to redo old oil burner furnaces to run this stuff. Not sure if he still does, but I am sure it would be worth looking into.