Scupper plugs are inserted during bunkering and some cargo operations. When removed, any water on deck can drain away - including any oily water. Oily water can easily be present on deck when, for example, plugs are removed from savealls during bunkering operations to drain rain water, in the event that it rains during bunker operations, or when loading/discharging dirty dry bulk cargoes.
The crew on one ship entered in the Association have devised and built a filter for fitting over each scupper. When the scupper plugs are removed, water can drain away from the decks only after passing through the filter. Click on an image to enlarge.