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