Thanks for your input everyone. I tried several of the suggestions about hanging, swinging and blowing out the tube, but there was still a thin cloud of condensation in the tube. Today I buckled and got a tube brush (like a bore snake) and it took take of things. I also got some cleaning tablets made by Nalgene, for both the bag and tube. Thanks!

If you look at blackhawk.com and look at hydrastorm accessories, you'l find a cleaning brush for your tube (and many other goodies)