Shows level of sewage in your holding tank. This 2" gauge can be used with any length Wema holding tank sensor. A High Level Alarm Module and a warning buzzer are available as options. While the gauge is very accurate, note that if you follow the Holding Tank Sensor installation instructions and choose a sensor length that only reaches 3/4 of the way to the bottom of the tank, the first 1/4 of tank contents will not register on the gauge.