If you are thinking about keeping just the old tank as a second receiver and you are concerned about the integrity of the tank, there are two ways to proceed. First pull out the inspection plugs on the side of the tank and look. The second is to find someone with a ultrasonic cylinder bore thickness gauge and see what the metal thickness is on the very bottom of the tank. I just bought a used 80 gallon horizontal tank to use as a second receiver and the seller pulled the plugs for inspection before I bought it.
