distal end of the plug a slight radial expansion occurs upon an axial compression of the sealing plug 6 so as to create a slight bulging of rubber into each axially elongated substantially rectangular equal distribution port 22 24 42 44 after collection of a urine specimen the cap 4 is placed over the base cup 2 and turned clockwise approximately 1 16 of a turn until the twist lock cap tabs 10 engage against the twist lock cup tabs 12 as discussed hereinbefore the opposed ramp surfaces 13 and 17 act as the first engagement means to force the cap axially down and squeeze the annular seal 5 down against the upper edges of the cup 4 the downward extensions 15 prevent over rotation and will frangibly break off if an over rotation is forced the first engagement mode occurs simultaneously at all mating locking tabs 10 12 only a short rotation is needed to force the cap down since each cap lock tab 10 initially is located in a resting position on top of one of the circumferentially disposed cup ratchet guides 26 as shown in fig3 the vertical clearance space 28 below the bottom edge of the extension 15 is not sufficient to pass a cap locking tab 10 past the point of total ramp surface engagement shown in fig3 a second engagement means is simultaneously supplied by engagement of a continous male thread member 48 or discrete extending.