Well I did post this a long time ago and it did become a sticky (long ago enough that all the referenced images vanished):
http://www.thorforums.com/forums/f8/...ific-2448.html
I believe that Ed took it and put it in the Axis/Vegas manual including the images.
Sure its Axis/Vegas specific but the procedure is pretty much the same for any motorhome. You just have to find all the mentioned parts.
If you have the Thor diagrams, specifically the plumbing ones, they do list where the low point drains and all the valves
should be.