Marine Toilets: Everything You Need To Know

A marine toilet is has several components and what we consider to be a “toilet” is actually the least important element when it comes to maritime laws. As you’ll see further in this article, maritime law focuses on the storage and treatment of sewage with your Marine Sanitation Device (MSD). For starters, lets look at the element of a toilet that land-lubbers are familiar with, the toilet bowl.

Marine toilets are designed to allow for sanitary conditions while out at sea. It should be evident that a traditional toilet would not work well on a boat. Consider a rough sea and the boat rocking heavily. A traditional toilet would have water spilling from the toilet bowl as the boat rocks. Conversely, marine toilet bowls a kept dry until such time that they are being used, then water is pumped into the bowl.


The toilet pump comes in two basic styles, electric or hand-powered. The basic concept is the same in both cases, they pump water into the bowl or out of the bowl in two different operational modes, “wet” or “dry” pumping.

“Wet” Pumping is the terminology used to indicate that you are pumping water into the marine toilet bowl. Essentially, water is pumped into the boat from the sea through a hull fitting called a seacock.[1] The water is pumped into the bowl prior to use and immediately after use to create a “wet” toilet bowl setting that we are accustomed to in traditional land based toilets. The pump brings water into the bowl with every down stroke and it sucks water out of the bowl with every up stroke. The existing water & waste pass through a “joker” valve.[2]

“Dry” Pumping is the term used to indicate that you are pumping all the water out of the bowl so you do not have water spilling over the edges of the toilet bowl while the boat is swaying or pitching.

Storage is the element of a marine toilet that needs serious attention. This is where the maritime laws come into play. Basically a toilet flushes the waste into a storage tank which makes up the main focus of the balance of this article.

Marine Sanitation Device (MSD):

A Marine Sanitation Device or otherwise known as MSD is defined in the Federal Water Pollution Act as “Any equipment for installation onboard a vessel that is designed to receive, retain, treat or discharge sewage, and any process to treat such sewage.”[3] This leads to some level of confusion because a fixed mounted toilet on a boat, known as the “head” as well as Coast Guard Certified Type I, II or III MSDs, units that not classified as the head, are also MSDs according to the Federal Water Pollution Act.

One clarification point:
The typical head (marine toilet) on its own has ever been made that is Coast Guard certified. The way the Coast guard looks at MSDs is that the head is strictly the component that receives and discharges the sewage. The components that treat the sewage are considered to be Type I and Type II MSDs. This treatment component is separate from the head and these components are the elements that are certified by the Coast Guard.

Upon Further Examination of the MSD:
The Federal Water Pollution Act has two key words that need some elaboration, “installation” and “sewage.”

Installation Nuances:
When a “toilet” is not secured to the boat, it is not regulated under the current Federal marine sanitation law. For example, if you have a bucket on your boat that is used as a “toilet”, then it is not regulated as long as the bucket is not being used to retain sewage over a long period of time. However, boaters need to be aware that the MARPOL treaty prohibits the dumping of any raw sewage into water within the US territory.[4]

Sewage Clarification:
Sewage is defined in CFR 140.3 as, “human body wastes and the waste from toilet and other receptacles intended to receive or retain body waste.”[5] When is pertains to maritime law, sewage is strictly human bodily waste and does not include items such as galley water, food, oil, etc. However, the Great Lakes do require that “grey water” be held. Grey water is water used in showers, baths and in the galley.

Coast Guard Type I, II and II MSDs:
The first point to remember is that the Coast Guard doesn’t care about the toilet. They view MSDs as the device where the toilet flushes into. Basically the Coast Guard is concerned with the holding and treatment of sewage.

Rob Cozen for the does a nice job explaining the differences in Type I and Type II MSDs as shown below:

A Type I MSD must macerate (a macerator is essentially a “blender”) to no visible solids—in other words, totally liquefy solids and paper, and reduce the bacteria count to less than 1,000 per 100 milliliters. The discharge from a Type II MSD must contain less than 1,000 parts per 100 milliliters suspended particulate matter—in other words be almost absolutely clear (though not necessarily colorless)—and the bacteria count must be below 200 per 100 milliliters. A Type III MSD is a holding tank—any holding tank, including the holding tank in a portapotty.

Vessels up to and including 65′ may use a Type I, II or III; vessels 66′ and over must use a Type II or III. Because a Type II is so much bigger, so much more expensive, and draws so much more power than a Type I, you aren’t likely to see a Type II on a vessel smaller than 66 feet.[6]

Regardless of the type of marine toilet that you have, it is always a great idea to discuss toilet ettiequte with your guests when hosting people on your boat. Instruct them on the proper way to use the pump and remind them that the only toilet paper that should be used is biodegradeable!

Keep in mind that the fines for overboard discharge of untreated sewage are constantly rising. Additionally, get in the mindset of protecting the environment. Learn where the local pump-out facilities are located. Some other tips for marine toilet maintenance include cleaning. We have found that mixing a solution of one part bleach to 10 parts water kills any bacteria during your cleaning process. One last point, prior to hauling out you boat for the season, flush, clean, and pump dry the holding tank. When the boat is land, completely drain any remaining water in the toilet to prevent freeze-up damage during the winter.



[3] (10 pp, 170 K).