A combined plug and sealing ring for a sprinkler nozzle includes a nozzle plug having a substantially cylindrical portion adapted to engage within a nozzle orifice of a sprinkler nozzle, and a cap overlaying the substantially cylindrical portion. A sealing ring is adapted to seat onto a threaded pipe fitting portion of the sprinkler nozzle. A leash interconnects the nozzle plug and the sealing ring. A combined plug and sealing ring in combination with a sprinkler nozzle, and a method of installing a sprinkler nozzle in a highly corrosive or extremely corrosive environment are also disclosed.