Is it possible to detect a 24x48 oil heater oil tank with a metal detector? How deep could it?

I'm buying a house, and it's not certain if a tank was removed from the yard. The owner is being evasive about it. It's in his best interest NOT to find out, because he'd have to do something about it. If he knows there is one before we close on the house, it's his problem to deal with. The structural contingency for the purchase contract has elapsed so I have little recourse.