Abstract: A temporary plug for insertion into an open end of a conduit for gaseous fluids comprises an imperforate body having a fluid tight distensible member which is arranged to be enlarged by the introduction of fluid therein, and to seal against the inside surface of the conduit and plug the same. A flexible vent tube has one end connected with the plug body, and the other end positioned at a location remote from the open end of the conduit. The vent tube communicates the gaseous fluids with the atmosphere at the remote location to prevent leakage of the fluid in the vicinity of the plugged end of the conduit.