Oil tank inspection

[Qamar U Islam]

Hi, long time reader first time poster here.

I am buying a 1902 multi family house in New Jersey. Sellers mentioned the unit had an above ground oil tank that was removed and there is visible signs in the basement of plumbing for an oil tank. My question is can there also be an underground oil tank? Sellers don’t know if there ever was one of those. I had an oil tank sweep that came up negative but the inspector could not get under the front porch because they would have to break down part of the porch to do it. Should I ask sellers to open it up for us? How likely is that there is an oil tank there? I don’t want to be left with a bill later on if it ever comes up that there’s contamination.

Thanks for your help.