Been doing it regularly for 20 years about every 2-3 years as my tanks that I have get bad looking. All they care about is the fact you turn an old empty tank in when you get a new filled up tank. What you have to do is check out the best looking new filled tank out when you exchange your old tank. Remember, they clean and most of the time paint your old tank before they fill it and put it back on the market again. So check for rust and espcially discoration in the tank nozzel and handle to see if it is a newer tank. There's also a date of manufacture on the tank to see how new it is. Check for the location on your old tank and it should be somewhere in the same general area on the tank you are getting from them.