Snowman9000 - My floorplan is a little different than yours, but you are correct someone did not know how to winterize. The first couple years, I poured about 2 gallons of RV antifreeze into the fresh tank. Made it easy to pump the pink stuff through the plumbing. Was not that much of a problem, in the spring, to fill the fresh tank with clean water with about a 1/4 cup of Clorox and drain. I later installed the 3-way valve and siphon tube between the fresh tank and the pump. I still flush the fresh tank with Clorox.
There have been postings about installing a drain valve on the water heater using an adapter, but I concluded if I ever had to remove that it could be a real problem. This way, I just easily remove the plastic plug and replace. I have carried a spare since we bought in 2002.
burlmart - Hope you escape any further destruction and turmoil with the tropical storm Isacc.