You trade in the empty tank for a refilled one at Lowes and Home Depot. The tanks are then sent to a company like Blue Rino who tests, recertifies and refills the tanks to send back to Lowes to resell to you when you trade in your empty tank for one of their filled ones. If you do not have a trade in then they charge you up to $40 for a replacement tank and $22 for the gas fill. With a trade in tank you only pay $22 for the gas. Hope this helps you understand why an old empty tank is still an asset. Save some $$ and recycle an old tank. Good luck saving money.