Seems to me the overflow drain tube would have no problem also venting vapors.
Weather/overflow can't vent vapor. That gas cap has a rubber seal over the filler neck. Any escaped vapor is going to vent out and around the beauty ring, as would water enter the same way. So if that weather tube would vent, here comes the water and/or water vapor into the tank and rust assured, use is going to fuccup the fuel pump with rust remains rotting the ceiling anshit.
If say I walk up to any gen gas tank, read the number of tubes at the back of the tank:
1. Single tube at back of tank = Not counting the weather tube... New evap control system. This is the overfilled vent tube heading into a charcoal canister and evaps out #4 throttle body vac tube.
2. Double tubes at back of tank = Not counting the weather tube... Conventional evap control system. This uses 3-4 throttle body vac tubes. Middle tube has vapor/liquid exit tank. Enters a separator via a pump pulses off the the vacuum of(3) throttle body. Gas-returns to far right tube. Vapor exits out to (4) throttle body's vacuum.
Cali/other style Tanks w/nipple recess = Find the nipple hole at tank filler neck. Use cali gas caps. Or run a race gas cap on any tank.
A Good Sign--reading the gas cap = Dual balls can keep the pressure in so that whoosh out the cap when keyfobbed is turned, we are not at 14.7 pounds to lift ball, but the whoosh was that building of pre-pressure.
I blow in each tube and find where the other end is and decipher who is whom. I then finger close the hole, blow into the tube again so the tube is not split so I have pressure present.
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