Leasing a tank is different, the owner is always responsible for inspecting the tanks, you might find a fly by nighter that doesn't inspect them once they are in the field but with one accident they will be gone! Yes the tank rules would be federal, look on the neck of the tank and you will see an inspection date and what type of inspection was performed, not performing the proper inspection puts the tank owner at risk in the event of an accident. Filling a tank owned by another propane company is illegal, if the tank is owned by the homeowner then each company that delivers to that tank is by law required to do a leak check on the entire system by doing a pressure drop test, most companies charge for that service.