Waterway Crystal Water Cartridge Manifold Plug (519 4320) gfci The Raypak pressure switch tube The Raypak pressure switch tube is designed for compatible 183A and 185A heater applications where the supported pressure sensing connection tube needs replacement and WB compatibility give this plate practical value because skimmer vacuum accessories work best when they match the original skimmer opening and seating relationship closely especially in filtration systems where a missing or damaged plug can interfere with proper reassembly A manifold plug like this is an important service part because it helps complete and seal the manifold area properly