the tank has to be dug up ! dont buy unless it is!
all the advise here is correct ! I went through this we bought a house 20 years ago and when we went to sell the tank that was "decommissioned" still had sludge and contaminated the soil we were so "lucky" that we were close to a neighbor and because we contaminated their soil insurance covered the clean up. thought i was never going to sell that house!!