An oil stop valve assembly for allowing a flow of water and blocking a flow of oil has a body having an inlet and an outlet, a seat formed adjacent to the outlet of the body, and a float positioned in the body. The float has a specific gravity of between 0.90 and 0.95 so as to be buoyant in water and to sink in oil. The float is away from the seat when a level of water within the body is above the seat. The float is seated in the seat when the level of water in the body is adjacent to the seat. The body is positioned in a container having a fluid inlet and a fluid outlet. The fluid outlet of the container is connected to the outlet of the body.