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Marine Sanitation Devices

Marine sanitation laws for vessels with permanently installed toilets have been in effect since 1980. However, 20 years later they still cause confusion among boaters and communities trying to enforce federal laws at the local level. Marine Sanitation Devices (MSD) are part of a system that consists of a toilet and a sanitation mechanism. MSDs, as defined by the Federal Water Pollution Act, are devices that receive, retain, treat, or hold sewage. Under this definition, toilets would be considered MSDs. The problem with this is that there are no Coast Guard approved MSD toilets.

To complicate the matter more, there is a growing number of federally mandated No-Discharge Zones (NDZ), which are bodies of water where no sewage, even if treated by a Type I or II MSD, can be discharged from any vessel. This restriction does not apply to "gray water" for recreational vessels, which is waste from sinks and showers. Most inland waters and lakes of the United States are considered No-Discharge Zones.


All Coast Guard certified Type I and II MSDs have a certification sticker on the device placed by the manufacturer. No sticker? Not approved and therefore not legal.

  • Type I units reduce bacteria to specified standards and discharge treated waste directly overboard after macerating (grinding) the waste, leaving no visible solids. These systems are for boats 65 feet or less. Type I MSDs are not legal in federally designated NDZs.
  • Type II devices are the same as Type I devices, except the standards for treatment are higher. These systems are for boats 65 feet and larger and require more electrical power to operate. Type II MSDs are also not legal in federally designated NDZs.
  • Type III systems are holding tanks in which the toilet flushes directly into a container instead of overboard. This system is the only one that can be used in all waters. Holding tanks can be discharged at pumpout stations found at public and private marinas, and beyond the three-mile offshore limit.


  • Macerators do not treat sewage—they only grind it. They’re only legal if used to pump out a holding tank when outside of coastal waters.
  • Y-valves allow bypassing the holding tank for direct discharge and may be used in the open position if outside the three-mile discharge limit. They must be secured in the no-direct-discharge position when within the three-mile limit. Permissible methods for securing the Y-valve are by padlock, a non-reusable wire tie, and removal of the handle.
    Portable toilets with built-in holding tanks are perfect for smaller boats.
    Portable toilets provide an option for vessels that sail a variety of waterways, and those boats that don’t have the space for a Type I, II, or III MSD. Portable toilets are legal on all waters because they are not permanently installed, and therefore don’t fall under the Coast Guard rules. The holding tank is usually built into the bottom of these devices, and contains a few gallons of water and chemicals for treating the waste and flushing. The waste can then be carried ashore and disposed of in shore-based sanitary facilities. The drawback is the minimal holding capacity and the need for frequent pumpout or disposal.

  • Type I & III combinations provide the most flexibility for sewage disposal. The Type I MSD can be used to treat the sewage and pump it overboard in areas that are not designated NDZs, and the holding tank (Type III MSD) is legal and can be pumped out at onshore facilities if in an NDZ. When offshore, outside the three-mile discharge limit, either device is legal and the holding tank can be bypassed, with a Y-valve set for direct overboard discharge.


The system that you install should reflect how the vessel is used, including the following:

  • The period of time the vessel is used. A portable toilet may be perfect for daysailing, a small holding tank should suffice for overnights, but a large holding tank and/or a Type I or II MSD will probably be necessary for long cruises.
  • The number of crew normally carried on board—the more people, the more capacity you will need.
  • How often marinas are visited where shoreside facilities can be used, as opposed to anchoring out where the onboard sanitation system will get more use.
  • The availability of pumpout facilities where you sail—if they are few and far between, a larger system will be required.
  • Whether the electrical system is capable of handling a Type I or II system. This is mostly a cost issue as the electrical system can always be enlarged to handle the extra load.
  • Space available to accommodate MSD or holding tank installations.



Each MSD, or combination of MSDs, required different skill levels to complete the installation. The easiest is the portable toilet, which may require little more than mounting some hold-down hardware. Holding tank installation may be relatively simple if a flexible tank is used, needing only enough skills to make multiple hose connections and the mounting of deck pumpout fitting and overboard vent. Rigid holding tanks may require additional woodworking or fiberglass tools and skills, but not at a highly sophisticated level. Type I and II MSDs require the same skills with the addition of some electrical aptitude and a more complete toolbox.

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Kathy Barron is offline  
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