The Bilge Boy is a two-stage gravity/coalescer type bilge oil/water separator. The first stage of the system is the gravity separator. Water is drawn into the unit by suction where large oil drops rise to the top of the housing due to the lighter density of the oil. Smaller oil drops flow down and out at the bottom with the water to be removed by the coalescer stage. The coalescer is the second stage. The bilge water with remnant small oil droplets flows through the element. The tortuous paths of the element catch the oil drops, while the purified water flows through to be discharged overboard. The oil caught in the element collects, or coalesces, with other oil as it moves toward the outside of the element. When the drops release, they rise to the top of the coalescer housing where they are circulated to the gravity separator chamber for discharge to the oil holding tank.