The attached link shows that the Anderson Valve, in the Sanitize/Winterize position, isolates the fresh water tank from the system - not allowing anything into the fresh water tank. Therefore, it seems that you can sanitize your lines, but not the tank. The only method I can think of (not wanting to pour bleach into a hose) would be to use a standard home water filter, remove the filter element, put a diluted solution into the bowl, then carefully screw the bowl back onto the header and force the solution into the water tank in the 'Tank' fill position. Since I use a 'house ' style Culligan filter when camping to remove odors and sediment, I am not adding any equipment,just finding a new use for what I have.
Additional Information: Received a phone call from JD Adams at Heartland this morning. The Anderson 4 way valve will not allow Sanitizing the freshwater tank! His suggestion is to use something like a Miracle Grow chemical dispenser that hooks up to a garden hose and meters the chemical into the water tank with the valve in the Tank position. I'll stick with my water filter method above.
I also asked about how to tell when the fresh water tank is full (if uncertain of the accuracy of the monitor panel) since there is no vent line running to the Universal Docking Station on my Bighorn. His response was that the vent line is now routed to the underside of the trailer and when the tank is full, will vent to the ground under the trailer. Don't know exactly where, but will attempt to find out when Wisconsin weather allows me to de-winterize the trailer. Hope this is of benefit to other Bighorn owners - answered many of my questions.