That, my friend, would be a very dangerous misapprehension. Any discharge of sludge, oil, oily waste and water with more than 15 parts per million (PPM) of oil or other pollutants is strictly prohibitet under MARPOL and national laws. In particular, these violations have been intensely prosecuted by US authorities. US authorities have ways to prosecute these crimes also if they only happen in international waters.
I have worked a lot with these cases and will find time to write more fully on this very important subject later, as voilations like the ones MSC, NCL, Evergreen, Carnival Cruise Line, AP M