An adapter includes a base connectable to an anesthetic agent container, a spout that extends from the base and defines at least one flow path therethrough, and a valve assembly disposed within the at least one flow path, the valve assembly being moveable between a first open position and a second closed position. The adapter also includes a radially expandable seal disposed about the spout, the seal having a first end, a second end, and an intermediate region between the first and second ends that expands radially outward relative to a longitudinal axis of the spout. The valve assembly has a surface that cooperates with the seal, wherein the cooperation between the surface and the seal expands the intermediate region radially outward relative to the longitudinal axis with the valve assembly in the first position.