Topping off the gas tank isn’t just bad for the environment, according to the U.S. Environmental Protection Agency (EPA), it’s also detrimental for your wallet. Because the gas nozzle automatically clicks off when your tank is full, topping off can result in your paying for gasoline that is fed back into the station’s tanks via the pump’s vapor-recovery system, which prevents gas vapors from escaping into the air and contributing to air pollution. In fact, topping off might even foul up the mechanism and cause not only a gas-pump failure, but also a potential air-pollution problem. See the permalink for more information.