Originally Posted by f1100turbo
Thanks for the photo. What is pictured is the hat and cold cut off valves to shut off the water supply from entering the water heater. The one that connects across (in parallel with) the water heater is the bypass valve.
In the summer (normal camping mode) the bypass is CLOSED so water goes in and out of the heater.
During winter, the bypass is opened and the input and output valves are closed. This allows the introduction of anti freeze to get to the HOT water side of the plumbing without going through the heater.