1997 Nissan Sentra fuel system is flooded

The car didnt want to star I check for the spark plug if they have spark and they do have spark but they were full of gasoline I replace the fuel pressure regulator to see if that was the problem buy that wasn't the problem is that the spark plugs get full of gasoline I check for the return line and I blow it with my mouth and it feels like is clogged them I opened from the fuel tank cover and every time I blow gasoline comes back and I don't know how these system works from others if is right or is not sopposto return gas