This permits introduction of a resilient cap, which will secure the connecting sections within the hollow and allows {HEAD ~ otherwise trapped air} to escape readily through {TAIL ~ the opening} 
to escape readily through
This permits introduction of a resilient cap , which will secure the connecting sections within the hollow and allows { HEAD ~ otherwise trapped air } to escape readily through { TAIL ~ the opening }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL