The tank level gauge consists of several sensors that are basically screws placed at strategic heights through the side of the tank. These screws are then connected to electronics that sense if there is a conductive path ( through the liquid in the tank). If the liquid level reaches the sensor, it illuminates an LED. These sensors are notoriously inaccurate as items such as toilet tissue can get hung up and cause the sensor to conduct and generate a false reading. The sensors can sometimes be cleaned with cleaning wands or various other cleaning methods. Most experienced RVers use a combination of sensor readings and gut feel of what the tank should read based on use.
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