a generally cylindrical closed ended molded plastic cap for use in a liquid storing container includes a planar sealing surface at the closed end which defines a tab recess . a substantially planar molded plastic tab configured to be pivotally mountable within the tab recess is snap fitted to the cap and is pivotable between a first position in which the cap seals the liquid storing container and a second position in which the liquid may be removed from the container . a pair of tines on the tab cooperate with a corresponding pair of grooves in the tab recess to resist stresses which tend to separate the tab from the tab recess .