{HEAD ~ an open top trough structure} providing {TAIL ~ a pooling space} in which feed material can pool 
providing
{ HEAD ~ an open top trough structure } providing { TAIL ~ a pooling space } in which feed material can pool
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH