It is common to have the tank level indicators in the control panel area. There should be a row of small push buttons with a row of small indicator lights. The push buttons should be labeled:
battery
black
gray
fresh
But also keep in mind numerous individuals have issues with the black, gray giving false readings, us included. What we do is listen for certain sounds to determine when we need to dump our tanks. For instance the black tank is when it "burps", the gray is when it "gurgles" time to dump.