I have a problem with my evaporative emission control system. I have Regina components if it is relevant.

For several years now, upon removing the cap to refuel, I've found the fuel tank under pressure due to gasoline vapor (perhaps ~10 psi). I guess this means that vapor is not reaching the charcoal canister.

On hot summer days, substantial amounts of gas vapor accumulates in the cabin when parked.

I've finally decided to fix this somehow! I've been all over this site without finding the documentation I need to proceed.

I've disconnected the line to the fuel tank (I think) at the charcoal canister, and wire-tied it out of harms way. Pressure still accumulates in the tank!

Is there a check valve that might have failed in this line or where it attaches to the tank (to the fill pipe I believe)?

What else might cause my symptoms?

If I can't replace such a check valve, my next question would be:
How many gallons per year of gasoline would I vent to the atmosphere (in North Carolina) if I were to just provide a small vent from the top of the tank to the outside air? If this is appropriate, what would be the best way to do it?

Thanks,
John