Don't flip the switch without water in the hot water tank. Assuming it is the electric for the hot water tank, (and it is in my rig) the element will be burnt toast in about 3 seconds without water in the tank to cool it.
Look under the rig and identify the dump lines for each handle. The size of the handle is not always an indicator of which line it opens. The small lines are generally gray tank and the larger line is black. In my case in the front compartment the larger handle goes to the gray tank and the smaller to the black. Pulling the wrong one will, in fact, be a "crap shoot".