An overcap is provided for use in sealing a container of the type having an outer rim, an inside wall surface, and an inner rim spaced inwardly from the inside wall surface, with the inner rim forming a container opening. A flexing portion is formed within the body portion of the overcap and is moveable between a first sealing position and a second sealing position. The flexing portion includes a downwardly depending wall member positioned adjacent the inside wall surface of the container in the first sealing position. A sealing plug is provided and is moveable between the first sealing position and the second sealing position. The sealing plug includes a peripheral surface dimension for frictional engagement with the inner rim, releasably closing of the opening in the second sealing position. The sealing plug is separated from the inner rim in the first sealing position.