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