One side wall of the housing defines {HEAD ~ an opening} through which {TAIL ~ the tubing reel} may be slidably removed 
One side wall of the housing defines { HEAD ~ an opening } through which { TAIL ~ the tubing reel } may be slidably removed
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH