Two things I'll add - while you shouldn't keep the black water tank valve open (as furpod said), it is ok to leave the gray water tank valve open. When the black tank is at least 2/3 full then close the gray tank and let it fill up (2-3 showers will do it, it doesn't take long). Empty the black tank first, then the gray tank (that will flush out the hose), leaving the gray tank open again.
My last TV (tow vehicle) had constant power to the Bargman so I always shifted the fridge to propane if we stopped for more than a half-hour and often wouldn't move it back until we got to camp. 12 volt mode uses about 10 amps per hour (not including the other 12 volt stuff like the LP detector) which is a significant draw if the engine isn't running. If we were camping with no hookups I would start off with the fridge on propane before we left and it would stay there until we got home.