Any detergent will emulsify oil
Engine degreasers, available from any auto parts store will even soften up oil that's turned into "bubble gum" enough to get it off with a scrub brush.However, as others have said, just emulsifying it and sending it overboard is a no-no. The pads won't work if the oil has been emulsified, so before adding any detergent, use pads or pillows--changing 'em as many times as necessary--to soak up all the oil...disposing of 'em as you would used oil (marinas should have a special disposal site). Once all the oil has been removed, use a strong solution of any liquid detergent or degreaser to clean the bilge. Really CLEAN the bilge, and rinse ALL the dirty water out. You wouldn't just dump some Dawn into a sinkful of greasy dishwater, or some Scrubbing Bubbles into a bathtub full of dirty water, then pull the plug and expect to have a clean sink or tub...you can't end up with a clean bilge that way either. Never use bleach or chlorine tablets in a bilge...it's murderous to rubber, including hoses and rubber parts in bilge pumps.