The apparatus further comprises an electrical circuit that automatically shuts off power to the liquid reservoir pump whenever the drain becomes obstructed, while energizing the pressure pump and opening {HEAD ~ the valve} to permit {TAIL ~ the generation} of positive pressure into the drain to dislodge the obstruction 
to permit
The apparatus further comprises an electrical circuit that automatically shuts off power to the liquid reservoir pump whenever the drain becomes obstructed , while energizing the pressure pump and opening { HEAD ~ the valve } to permit { TAIL ~ the generation } of positive pressure into the drain to dislodge the obstruction
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH