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Marine Sanitation Devices

What is a Marine Sanitation Device (MSD)?  It is any equipment installed on a boat designed to collect, treat, or discharge sewage and human waste that can accumulate onboard boats (recreational and commercial).

If you have a toilet installed on your boat, you are required to have a functioning, U.S. Coast Guard-certified Marine Sanitation Device while operating on U.S. navigable waters. This includes waters within three miles of the coastal shoreline.

A Marine Sanitation Device or (MSD) is defined as “any equipment for installation on board a vessel which is designed to receive, retain, treat, or discharge sewage, and any process to treat such sewage" (EPA MSD website). 

  •  Section 312 of the Clean Water Act requires the use of operable, U.S. Coast Guard-certified MSDs on board vessels that are 1) equipped with installed toilets, and 2) operating on U.S. navigable waters (which include the three-mile territorial seas). 33 U.S.C. 1322(h)(4) (PDF) (10 pp, 170 K). 
  • The MSD requirements do not apply to vessels that do not have installed toilets (e.g., vessels with "porta-potties").
In 2019, the Marine Board adopted rules (250-010-0010 definitions, and 250-010-0750) related to sewage collection and disposal for recreational marine sanitation devices at the state level. The requirements now mirror federal discharge regulations. It is illegal to discharge ANY sewage (raw or treated) into freshwater lakes, reservoirs, or other bodies of water where entrances and exits are too shallow for boats with installed toilets to navigate.

Image from BoatUS

The Flow Process

Once waste moves through an MSD, it meets a “Y-valve."  To prevent discharge overboard, the Y-valve must be secured in the closed position. While in the closed position, sewage is directed towards the opening at the deck level and a pumpout station can be used for disposal.

Remember, unless you are more than three miles offshore in territorial seas, it is against the law to discharge untreated sewage from your boat.

Three Types of Marine Sanitation Devices

On recreational boats, a Type III MSD is typically a holding tank that collects and stores untreated sewage. A pumpout station can be used to remove waste from a holding tank once you return to shore.

Type I and Type II MSDs are flow-through sewage treatment systems. Type I MSDs use maceration (a grinding or blending mechanism to reduce human waste to a slurry, which can then be moved by pumping) and disinfection. Type II use biological treatment and disinfection. More information on treatment requirements for these systems can be found here from the Environmental Protection Agency.