[Wardworks]

Unfortunately, that is only going to let out air not any condensation in the tank. Water settles to the bottom of the tank so the drain is on the bottom to drain out the accumulated water. The plug that you are draining from is half way up the tank so no water is going to come out of there other then vapor mixed with the air.

If you had 3 gallons of water come out of the other tank it probably had never been drained before.