Charcoal canister, help me understand.

Let's try this a different way.

How do you know it's leaving the fuel line? And, is it just leaving the fuel line between the carb and the fuel pump? Or is the entire line from the carb to the tank going dry?
I have a clear filter before the carb, and the gas siphons back once the car is turned off. It will run off the bowl, then stall. Usually have to crank for a while, id say up to 20 seconds before getting fuel back to the carb. Not sure if the capped purge on the canister is causing this or a tired fuel pump.