All boats with a permanently installed toilet are required to have a Type I, II, or III Marine Sanitation Device on board to collect and process the waste products.
Type I. A Type I MSD is often a physical/chemical type (macerator/chlorinator) that uses environmentally-compatible chemicals to break down the waste before discharging it into the sea. The discharge cannot have any visible floating solids and must meet bacterial health safety regulations.
Type II. Frequently installed in larger boats, a Type II MSD is commonly a biological (aerobic digestion) unit that further decomposes the waste than a Type I MSD. Effluent pumped overboard from a Type II MSD can’t have floating solids and must conform to health safety regulations.
Type III MSDs are often holding tanks to keep waste onboard until an adequate pump-out facility can be located. A Type III MSD prevents sewage (treated or untreated) from being pumped overboard.