Passively filter hydrocarbons from stormwater in outdoor containment products. Outdoor spill containment presents a challenge that is not seen indoors: rain. Unless outdoor spill containment is covered / protected from the elements, it is susceptible to rainfall. If a containment unit's sump gets filled up with rainwater, it loses its capacity to contain spills. In other words, for every gallon of rain in the sump, there is one less gallon of chemical / fuel / hazmat that can be contained. The Ultra-Self Bailer is designed to attach to any spill containment unit, typically by a bulkhead fitting. Rainwater drains through the bulkhead fitting and any residual oil, gas or other hydrocarbons is removed by the filter media inside of the unit, allowing only clean water to exit. In the event of a spill, the media swells, completely sealing off the self bailer preventing any liquid from escaping.