Sorry to bump an old thread..
We had our selector facing I think up or down although it only took from the front tank which is now empty.
If I turn to the rear it takes from the rear tank. Although now if I try up or down it takes nothing.
Would this be as the front tank is empty.. Or something setup incorrectly as it only seemed to take from the front tank.
We had problems away where we had no water from the mains.. Well it did then stopped. then started then stopped. Only use the water for sink and coffee so removed the mains and used tank water.. Then noticed the front tank empty
With the mains yes I checked the tap and hose, after the first day I just used the tank water.