geomcnasty

Hi everyone. I have been getting the PO442 EVAP code. Small Leak. I was wondering if anyone know exactly how the system works. I get the gist of it but every system is a little different. I changed the canister purge valve. That didn't help. I also replaced the hoses on the canister and a few other small ones. I understand that the system puts vacuum on the tank then measures the ability to maintain that vacuum to ascertain if there is a leak or not. I'm wondering about the fuel tank vapor valve? I pulled this valve and can blow air through in both directions. Shouldn't it not move air into the tank? I'm trying to figure this out and realize I probably need to smoke it but was trying to save that step.

Thanks.