Various bacteria, pathogens, and nutrients are present in human feces. Because of this, raw sewage and human waste can’t be discharged from a boat within US waters (inside the three-mile limit, out to 9 miles in the Gulf of Mexico) or navigable rivers. Federal regulations regarding sewage on boats are intended to prevent untreated sewage from entering our inland and coastal waters so that we will not have to swim or drink it.
Even though recreation vessels are not required to be equipped with toilets, all boats with permanent toilets must be equipped with a holding tank or sanitation device approved by the US Coast Guard. A Marine Sanitation Device (MSD) prevents human waste pollution if approved and operable.
The types of MSDs are:
Smaller boats under 65 feet in length may use a Type I, II, or III MSD. Any vessel over 65 feet long must have a Type II or III MSD. It is mandatory that all installed devices be certified by the US Coast Guard and should be marked as such.
Most inland and coastal waters require boats with installed toilets to have a sanitation system on board to control pollution. Some standards have been set by the Environmental Protection Agency, and regulations have been issued by the Coast Guard regarding the certification and use of Marine Sanitation Devices. Generally, sanitation systems include a head (toilet), a waste-treating device (MSD), and a holding tank.
IMPORTANT: The discharge of untreated sewage is only permitted beyond three nautical miles from the shoreline. A state or local law may impose additional restrictions on overboard discharges.