Hydraulically controlled container discharge lid to prevent spillage

A hydraulically expellable lid, comprising:

• a beveled plug member having an exterior circumferential surface exhibiting a first diameter substantially equal to an inner diameter of a neck defining an orifice into a flexible container closable by a cap providing engagement with an outer surface of the neck, and tapering to a second diameter less than said first diameter;
• an elastically deformable ridge superimposed around and circumscribing a central portion of said plug member between said first and second diameters, releasably engaging the inner surface of the neck when said plug member is forcibly inserted into the neck of the container, said ridge having a diameter greater than said first diameter, and releasably disengaging the inner surface of the neck when the volume of the flexible container is compressed;
• an upper lip extending radially outwardly from said first diameter of said plug member to beyond the inner surface of the neck of the container when said plug member is forcibly inserted into the neck of the container, with said lip forming a continuous surface exhibiting a greatest cross-sectional dimension that lies in a plane including the orifice and that accommodates said engagement;
• and
• an elongated tether attached at a first end to a surface of said upper lip exterior to said container when said plug member is forcibly inserted into the neck of the container and extending radially outwardly from said upper lip, and attached at a second end to one of the exterior of the container and the cap.