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