Drain valves

[RottieMom]

OK, I've been reading all the posts about the plumbing system with great interest... how to fill fresh water tank (with modifications and TM closed), how to drain system, etc. And, I just looked under my TM to locate the drain valves as shown on a diagram (that I think Bill did awhile back), and I only have 3 drain valves, not 4. There is one drain valve in front of the tire and two drain valves behind the tire, which I think are the hot and cold valves for the bathroom. The single valve in in front of the tire also has next to it what looks like an overflow tube behind a mesh screen.

My TM is a 2013 2720SL. So, do you think the single valve in front of the tire is for draining both the fresh water storage tank and the water heater? Or, do you think the water heater drains thru the bathroom hot water drain valve?

I'm really puzzling over why TM doesn't include a schematic of plumbing system in the Owner's Manual.

Thanks for any help you can provide.