The backflush pump draws the backflush fluid from {TAIL ~ the reservoir} at {HEAD ~ a defined time} 
The backflush pump draws the backflush fluid from { TAIL ~ the reservoir } at { HEAD ~ a defined time }
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD