[Kirby64]

There’s no ambiguity here. You own the 20 lb tanks. Now, after they expire most propane companies won’t refill them, but otherwise it’s yours to keep. You could argue that this isn’t actually “owning” it, but for all intents and purposes it is. You’re responsible for making sure it’s not expired when using it, although the companies that do all the exchanges are responsible for making sure tanks they sell are not expired.