Flapper door above, and get the replacement ac delco canister installed. It is pretty simple, but looks confusing with all the hoses. Here are two pics that might help you.
I WOULD NOT just delete the charcoal canister!!!! Not recommended. AC Delco makes one that is a pretty good fit, and there are ways to try to unbolck the factory one.
@Beehanger Have you looked at any of the Charcoal filter posts yet? If you have high pressure when you remove the gas cap it could certainly be your charcoal canister.