The Dometic/Sealand Duck Bill Valves Kit comes with two 1 ½” duck bill valves for “T” and “S” series pumps. These valves are a critical component of the VacuFlush system. They help maintain and generate the vacuum for the system and should be replaced frequently. Note that “S” series vacuum pumps, low profile vacuum pumps, and the VG2 vacuum pumps require 4 valves (2 kits). The “T” series discharge pump requires 1 kit (2 valves).