Will not draw gas through fuel lines

Craftsman LT1000 19.5 HP B&S V-Twin. I disconnected fuel line at carb & blew back through to ensure no blockage & then syphoned gas all the way through the line & it immediately drains back to the tank. I can see it through the filter. I poured a bit of gas directly into the carb & it started fine but would only run long enough to use up that gas. Filter remains empty.