Thanks for all of the input gang. Unfortunately, I've been all over this darn thing and I can't find any other valves or lines that I haven't already traced and identified, and none of them are what I'd consider a tank drain... This is our 4th RV so I'm pretty familiar with how things are supposed to work, and my typical draining and winterization plan is a mixed bag of a lot your comments and recommendations, so thanks again for all the input. I'm fearful that this may be an oversite by the factory...