In operation, the nurse or other operator removes the cap 262 from the extension wall 258 and rotates the extension wall until the key 254 and keyway 256 mate, at which time the extension wall 258 and base 246 are urged toward the pierceable stopper, until the hollow cannulas are moved from a first position illustrated in FIG. 16 in which they are spaced from the chamber 212, to a second position