1991 Ford F-250 No fuel

Engine Performance problem
1991 Ford F250 V8 Two Wheel Drive Automatic

Have dual tank system. Both tanks have gas and have b
been treated with drier. Has sat for 6 months with little
little fuel in one tank. Engine cranks fine. Will not fire - not even once. Poured gas directly in card. It ran fine for 15-20 seconds, then died. Did this twice and same results. Can't find fuel filter. Want to check it for (a) gas and (b) clogs. Recently switched from front tank to seldom used rear tank. Where is filter and what should be my check-sequence? Thanks.