Our coach has an Atwood water heater without an anode and our owners manual doesn't show an anode rod in the parts list. Maybe your Damon owner's manual was referring to a Suburban WH?
Your idea of leaving the WH plug out and flushing with lots of fresh water should do the trick to get the pink out. I also made a flushing attachment that fits on the end of a garden hose that I use a couple of time a year. It's basically a 1/4" soft copper line about 18" long with the end bent 90 degrees and pinched a little to make it spray. Just turn it on and shove it in the drain hole. A similar device is available from CW, but mine costs more. (Why buy it for $5 when I can make it for $8?)
Denny, Connie & Shadow (former barn cat made good)
2006 Tiffin Phaeton, Cat C7, Freightliner Chassis