2001 Ford F350 fuel tank

Engine Performance problem
2001 Ford F350 V8 Two Wheel Drive Automatic

was workg with diesel doc yesterday have &.3 turbo diesel died on hiway. Had tested electric pump on frame rail for power and ground. Yes to both power with key on approx 20 sec and good ground. The diesel
doc asked was fuel going thru pump. No fuel when pump energized added 10 gallons no change draw vacume on supply line from tank 0 inches vacume remove tank vac test supply line good help 20 inches vacume reconnect retest fail. Remove fuel module tank very clean no critters screen clean. There is a device that is on the supply tube and hosed to return side, what is this and to disconnect hose and draw vacume system passes vacume test. Any help would be greatly appreciated. Thank you manuel