Place oil absorbent materials or a bioremediating bilge boom in the bilge. Place an oil absorbent pad under the engine. Replace oil absorbent materials regularly. Look for contractors or marinas that offer a bilge pumpout service. Do not treat oily water with detergents.
Soaps pollute and make clean up impossible.
Alternatively, they should be double bagged with one plastic bag sealed inside of another and tossed in your regular trash. Bioremediating bilge booms may be disposed in your regular trash as long as they are not dripping any liquid. Because the microbes need oxygen to function, do not seal them in plastic bags. Hydrocarbon emissions contribute to ground level ozone, a known health risk. Too much oil can foul spark plugs and too little can lead to increased engine wear or even failure.