Immediately after use, and before disposal or storage, you MUST (1) spread out any greasy materials outside to dry by flattening them out to their full size in an airy area for 24 hours at temperatures above 40°F, or (2) fully wash them with water and detergent and rinse. If you do not, the oils will continue to spread through the environment. Dirty rags can be washed in hot water with a little soap. Make sure that you get all of the dirt and oil off of them because they will absorb more liquid if there is any left on them. After washing them in hot water, put them in the laundry right away with your regular laundry items or hang them up to dry overnight. If you don't want to wash them immediately after use, then you should still spread out any greasy materials outside to dry as soon as possible because they will absorb more oil if left inside. Oily rags should never be thrown out with household trash. Instead, dispose of them in a recycling center immediately. Unfortunately, oil-soaked rags cannot be recycled and must instead be disposed of in landfill sites. The only real way to prevent further contamination is by not putting oil-based products into your sewer system in the first place!