I turned the truck on last weekend, filled it up and took for a ride. once i entered the garage i heard a hissing out of the gas cap...pressure! i would like to see if my thinking is correct about how the venting will be fixed. I made sure the evaporator was free and clear. removed the broken/clogged check valve at the top of the unit. used that line that ran directly to the engine bay and put a FJ80 Charcoal canister up there. so the lines go like this... 4 from tank to evaporator separator; line at top of evap sep to "tank" side of charcoal canister. Now my gas cap reads "vacuum pressure" so to test my theory i took off a line and used my mouth the pressurize the tank. it built pressure and did not release it. moved the hose "from tank" to the "purge" port on the canister all is well but should i leave it like that? if enough force it applied to the "from tank" it opens up just not free flowing like the "purge" port.