In {HEAD ~ a pipe} to be used in {TAIL ~ the ground} as a culvert, the improvement comprising: 
to be used in
In { HEAD ~ a pipe } to be used in { TAIL ~ the ground } as a culvert , the improvement comprising :
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH