Had a Denali just before the Class A, and the line are beautiful RV's...
The water heater by-pass should already be part of the plumbing. Remove the panel protecting the rear of the heater (inside backside of the unit). There should be 3 valves to stop the inlet and outlet and bypass (red and blue lines).
Looks much like the photo here:
Where is the water heater bypass valve?
The easiest way to drain the water out is with the plug on the exterior.
Water pump is different from each model. Ours was under the kitchen sink.
Kim and Steve, Mustang LCDR (Ret), '07 Damon Outlaw #1193
I have seen gross intolerance shown in support of tolerance, Samuel Coleridge
WE LOVE OUR OUTLAW RV