DOMETIC CORPORATION Dometic Sealand Tank Monitor System DTM4 W/O Vent 313604002 Dometic Sealand Tank Monitor System DTM4 W/O Vent Patented tank cap with three probes. Four-light indicator panel. For holding tanks up to 23-inches deep. Installs on any rigid holding tank material. Operates on 12-volt DC current. Optional "full tank" shut-down relay available.