{HEAD ~ The backfill pipe installation assembly} uses {TAIL ~ a backfill hopper} to simultaneously install drainage pipe above the trench floor and envelop the drainage pipe in backfill material to maintain the drainage pipe at a constant height above the trench floor 
uses
{ HEAD ~ The backfill pipe installation assembly } uses { TAIL ~ a backfill hopper } to simultaneously install drainage pipe above the trench floor and envelop the drainage pipe in backfill material to maintain the drainage pipe at a constant height above the trench floor
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