Oil Tanker Sweep - New to this bizarre habit

[JP Larcheveque]

Hi all,

After browsing a bit in the forum I figured I might as well just ask my question here.

I am looking to buy a very old brownstone in Phili, it has an oil tanker in the basement and half of the house is powered by it. I will be getting rid of this and replacing it with a power aired furnace. My question is: Can there be a second oil tanker buried somewhere on the property I am unaware of? 

Any info on this is much appreciated. There is a lot of sh.t I have to worry about in London, but dead tankers was not of them.