Check that the electricity or power to the camper is on. Go to the camper's tank level light panel or gauges, typically found near the front door of the camper.
Press the indicator button or switch to turn on the series of lights indicating the water level of the gray water tank. Many campers have a series of up to four lights. The first three are typically green and the last red. If all four lights are on, the tank is empty. With each additional green light, the tank is one-quarter more full, until the red light comes on to indicate the tank if near capacity and needs to be emptied.
Go to the outer holding tank panel, usually located on the rear right side of the camper, and open the tank housing door. Locate the gray water tank, which should be clearly labeled. Unscrew the cap and insert a dry, half-inch dowel into the tank and pull it out. Look at the water level on the dowel compared to the height of the tank to gauge water levels in the tank.
