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