"Drain Valve" on 2011 View 24K

[David]

I’ve got a 2011 View Model 24K. It’s the one with the longer side out on the driver side which includes the kitchen as well as the living room couch.
The coach was winterized at the RV dealer some time ago. I’ve got the RV at home now and want to use it – so I need to flush any antifreeze out of the system and fill with water.
Apparently the “Drain Valve” is open because when I try and fill with water so I can flush the system -- the water runs out of the overflow hose as soon as I start filling with water.
The Plumbing section of the 2011 Operators manual said it would tell me where the Drain Valve is for my model of coach. It says it’s “beneath the removal access panel in the floor of rear passenger side storage compartment”. I found 2 valves under that access panel and I closed them (or so I thought) but the water continues to run out the overflow hose. I rotated the valves back the way I found them and the water continues to run out the overflow hose. Therefore there must be some other drain valve somewhere.
The operator’s manual doesn’t give me any other drain vale locations -- so does anyone know where that valve is?