TWIII Level Indicator Cap Without Vent | Dometic 313000355 22 in. non-vented holding tank probe cap provides tank level readings for Dometic TW and DTM tank monitors. Dometic holding tank level indicator cap Non-vented cap Patented 3 probe holding tank cap provides tank level readings to Dometic DTM holding tank monitors 22 in. version Installs in Dometic SeaLand tanks or any rigid tank with 3 in. FNPT opening Use P/N 307230272 holding tank flange kit if tank does not have a 3 in. FNPT tank access port