A valve (20) is provided for sealing an evacuation port (16) in a port area (18) of a wall structure (12) of a container. The valve (20) comprises a casing (22) having a shell portion (30) which is deformable from an open condition, whereat the shell portion (30) forms a chamber (32) over the port area (18), and a closed condition, whereat the shell portion (30) contacts the port area (18). When the shell portion (30) is in its open condition, gas exits from the chamber (32) through gas-releasing holes (24) in the casing (22). When the shell portion (30) is deformed to its closed condition, a port-sealing adhesive (26) adheres to the port area (18) to thereby seal the evacuation port (16).