I wouldn't worry about rust if they have had product in them. My only concern is safety Yellowgold said they all still have pressure on them. Unless you have experience with dealing with propane tanks under pressure I would STRONGLY suggest talking to the seller about your intended use and asking them to depressurize them. It could be as simple as just opening a valve and letting it blow. But if by chance one has liquid in it, you have a possibility of circumstances that may be quite dangerous.One problem you may have is getting a fitting the delivery truck nozzle can fit into easily. | 
Propane Tank/Diesal Tank
