The present invention provides a slider valve assembly for connection to a spout of an aseptically-packaged flexible container for filling and dispensing flowable material. The slider valve assembly comprises a cap member, a valve member, and an outlet member. The cap member has a central opening and is adapted to be secured to the spout of the container. The valve member defines one or more side openings in communication with a central bore, is slidable within the central opening of the cap member and is lockable into a closed or open position. The outlet member is detachably engaged to the valve member and is used for actuating the valve member. The outlet member also defines a hollow interior portion which is in communication with the central bore of the valve member.