About all the indicators do is tell you the tank is still there. When we had our NT, DW would wash and rinse the the dishes in a dishpan and then dump the water into the black water tank to give some relief to the grey water tank. With just two people, the black water tank will last a lot longer that the grey water tank. We also carried a portable tank I used to empty the grey water tank when it filled . . . never did have to empty the black water tank.