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