21″ Buna Manway Gasket (GSK-1019-0009). This is a Gasket for a 21″ manway on vacuum trailers and trucks. Used in industrial, oilfield, septic and hazmat industrials. Product material is buna rubber. 21″ manway gaskets are used on the manway lid or (hatches) constructed from 5/8″ by 5/8″ square buna gasket material. This manway gasket is compatible with part number PAF21G.