Abstract: An anti-pollution mechanism usable on the filler tubes of automotive fuel tanks to prevent vaporous hydrocarbons from escaping from the tank through the tube, especially at the instant when the closure cap at the mouth of the tube is initially opened such as required during refueling. A vapor escape line extends from the fuel tank to a vapor collection canister. A pressure-operated valve in the escape line is automatically opened in response to opening of the cap on the filler tube such that vapors and fumes escape through the line instead of flowing out of the tube mouth.