Elongated tub 16 has {HEAD ~ a pair} of upstanding {TAIL ~ sidewalls} 18, 20 and a pair of upstanding end walls 22, 24 
of upstanding
Elongated tub 16 has { HEAD ~ a pair } of upstanding { TAIL ~ sidewalls } 18 , 20 and a pair of upstanding end walls 22 , 24
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH