"I think this is one of those situations where it's best to do it right
and not have to worry about getting caught up in a sticky situation
down the road. "
That's correct. If John listens to guys like Mark, with his advice to
just fill it with sand, he's likely looking for big trouble. When it's
time to sell the property, any buyer with common sense is going to be
alerted to issues of existing underground tanks by the likes of
realtors and home inspectors and it's very likely going to be a
condition in the contract that the seller stipulates they either never
had an underground tank or to prove it was properly handled.
Companies that do this professionally test the existing tank first, to
verify that it was not leaking. Then, they pump it out, cut it open to
remove sludge, and then either fill it or remove it. At the end of
this, you have certification that it was dealt with properly and there
is no contamination issue. And I would carefully evaluate the cost to
have it removed versus filled. If it can be removed for not a whole
lot more, I'd go with that, as it's going to be even more attractive to
a future buyer.