To protect the baseplate, it is shipped with a cover, also called a “flush cap,” held in place by a universal ring nut. There is a large O-ring (about 1 inch in diameter) between the baseplate and the flush cap. Sometimes this O-ring falls out, leading the user to question if the O-ring should be on the baseplate when attaching a filter. The O-ring should stay with the flush cap. If the O-ring is left on the baseplate, the filter will not seat properly and there will be no flow through the system. The proper procedure is (1) unscrew the universal ring nut, (2) remove the flush cap and O-ring, (3) attach the filter cartridge, and (4) then secure it by screwing the universal ring nut back on the assembly.
