{HEAD ~ A pair} of right and left main pipes and or a pair of right and left down tubes, or a main pipe and a down tube are formed of {TAIL ~ one piece} of continuous pipe material with its intermediate portion warped 
are formed of
{ HEAD ~ A pair } of right and left main pipes and or a pair of right and left down tubes , or a main pipe and a down tube are formed of { TAIL ~ one piece } of continuous pipe material with its intermediate portion warped
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH