Abstract: A tool and a method for installing a seal in a fitting through which gas is flowing is disclosed. The tool has a sleeve with a first socket that receives and holds the seal, and a second socket, adjacent to the first, that receives the fitting. A shaft is axially movable within the sleeve and has a contact surface at one end engageable with the seal. The shaft has a conduit with an inlet in communication with the fitting and an outlet that vents to the atmosphere. The seal is loaded into the first socket, the second socket is engaged with the fitting, and the shaft is advanced to push the seal from the first socket into the fitting. Gas flowing through the fitting is conducted to the atmosphere by the conduit, preventing gas pressure build-up behind the seal.