I have a DPP 50. When I first purchased the unit I used the steamer all the time. After a while I started to think about the fact that I can't clean the steaming chamber out. I stopped using it and I am curious if you guys have any thoughts about on the matter. I would think that there has to be rust in the tank?
I would love it if there was a drain so that it could be washed out.
That's a good question and one I didn't consider much until now. While working 'em I never noticed any kind of rust in the cooking chamber (which is probably why I never considered it) but now that I think about it there should be no rust (or very little) if it's dryed out which it would be after you run out of water at the end of a cook and you keep the cap on so air doesn't circulate through the tank. Secondly, after putting in our water well (the casing is iron pipe) we were told that rust scale will build up on the pipe and that's a good thing as it gets rid of the metallic taste. If your really worried I'm sure you can rinse out the tank by lifting the front of the trailer a bit and keeping a towel wrapped hose (so it seals) runing in the tank.
As for other impurities remember your dealing with steam where it exits the tank which should purify the exit as it runs (We used to get the steam runing for a bit before adding any food to clean it). This is not to say that I'd leave water in it between cooks 'cause I think you'd be risking undue levels of bacteria.
Personally I loved the steam, it seemed to speed up the cook a bit, it gave you the flexability or safety cushion in case you forgot to baste or got hung up doing something else and in my mind more moisture is usually not a bad thing.