Put a siphon tube in the 20. Buy a 5 and run that. Fire supply company will do that and give it a fresh hydro date cheap. Remember though you won't be able to run beverage off the 20 anymore. I'm looking in a cheap way to refill paint ball bottles adapter wise. They would only be good for serving already carbed beer but that would leave the 5 available to carb something else.
When i lived overseas i must have heard this joke a 1000 times "what does american beer and having sex in a canoe have in common? " . Both fu#*n close to water.