Abstract: A closure apparatus for a container includes an adapter which is mounted on or otherwise integrally formed with the container adjacent the container opening, and a cap which is moveable between an opened position and a closed position over the container opening. A coupling mechanism is provided for interconnecting the cap to the adapter so as to enable the cap to slide relative to the adapter between the opened and a closed position. A clamping mechanism, preferably provided by opposing ramped surfaces on the adapter and cap, is provided ton cooperate with the coupling means whereby the cap is urged into pressing engagement with the adapter over the container opening as the cap slides into the closed position.