I have a '71 Cutlass Supreme with the gas tank vent tube behind the rear seat back. This tube assembly has always sort of mystified me. Is it actually venting gas vapors into the interior compartment? Isn't that rather contrary to common sense?! Am I misundestanding its function?

 

Why, yes. Yes you are.

Here is what your Chassis Service Manual has to say about the Fuel Standpipe:




It is essentially a device for encouraging the precipitation of gaseous fuel into a liquid, and its subsequent return to the tank to be used.

- Eric

 

No, it does not vent vapors into the car.
It has to be high enough to keep liquid fuel from getting into the vent lines no matter how hard you drive, how steep the inclines are, or how hard the bumps are. Therefore the separator is up there high.
It gets its name as it also separates liquid fuel (that evaporates and condenses int he can) and routes the liquid back into the tank. In my car the actual vent opening is at the charcoal can under the hood.
At least that what I had understood anyway...