A fuel supply device includes a return fuel utilization buffer jar that conducts fuel into a fuel inlet port of a first three-way valve including a one-way check valve to allow the fuel to flow, uni-directionally, from the fuel inlet port to a fuel outlet port. Return fuel from an engine is conducted in through a return fuel inlet port of the return fuel utilization buffer jar. Fuel vapor in the return fuel utilization buffer jar is guided from a gas inlet port of a second three-way valve through a gas outlet port to a fuel tank. Vapor pressure in the return fuel utilization buffer jar is regulated by a ventilation port that is mounted in the second three-way valve and includes a one-way check valve in a direction toward the gas inlet port.