Tank Monitor panel indicates when a wastewater holding tank is almost full. This monitor helps prevent damage to the boat that can happen because of accidental overfilling of the holding tank. DTM01 Indicator Panel The indicator panel has a single red light which is activated by the float switch inside the holding tank. When the Full Tank light is activated the operation of any plumbing fixture connected to the holding tank should stop until the tank is emptied. Panel measures 3.25" wide x 2" high.Probe Assembly with Float Switch The probe assembly installs into a 1.25" dia. opening on the top of a holding tank. As the level of holding tank contents rises the float switch inside the tank is pushed upward and activates the Full Tank light on the indicator panel.