Greywater, engine cooling
water, deck wash down, et cetera, are all exempt for "no discharge" rules and regs. Generally speaking, the only discharges regulated are those involving anything that has passed through your body. However, the way the rules are written, peeing or pooping directly into the water is also unregulated. It's only when wastes enter some sort of containment system (be it a $3 bucket, or a $3000 onboard treatment system) that they become regulated.