My Big Horn is a different year and different model than yours, but perhaps similarly set up. There are two valves in the universal docking center. A diagram decal next to the valves show their off position and drain position. Move the valves to the drain position, turn on the water pump switch and the fresh water drains out. I quickly figured out the valve positions, but the water would not drain. I don't know what made me go inside and turn on the water pump, but that did the trick.