a biasing member adapted to apply force to {HEAD ~ the stopper} for pulling in the stopper into {TAIL ~ the receiving portion}; and 
a biasing member adapted to apply force to { HEAD ~ the stopper } for pulling in the stopper into { TAIL ~ the receiving portion } ; and
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH