The fuel pump itself has a check valve in it, so perhaps you need to rebuild it. The kits seem kind of pricey but they will have the new diaphragm material which is resistant to ethanol and it is a pretty easy job to do. Pay attention to which direction the check valves are installed. My trucks can sit for a least a couple of weeks before the gas in the carb bowl gets low enough that you have to crank excessively for them to start.
Regarding the "air" in the fuel filter that is normal and is not a contributing factor to your problem.
Kent
