I've just been looking at drain valves, and having some trouble with the logic. Obviously water condensates on the inside of the tank, slips down the sides, and pools in the bottom. ...to then be let out of the drain eventually. What I can't see is how frequency of draining will make any difference at all to how quickly the tank rusts. If you drain the sump once every hour, the walls of the tank will be wet with condensation, running down to the sump, to be drained very soon. If you drain the sump once a month, the walls will still be just as wet or otherwise with condensation. The only difference is more water in the sump. Either way, every single cool surface inside that tank is going to be beading with water. So what's the thinking behind auto drain valves? Thank you.