Houseboat Marine Toilet

It seems the smaller your boat is, the more you have to use your “head.” No, not the one on your shoulders. I mean the marine toilet or the houseboat “head.” And when installing a marine toilet or a houseboat toilet there are several types to choose from. The right system can make all the difference when it comes to enjoying your houseboat. The US Coast Guard and Federal Law have very strict rules about this subject. For most American waters, long gone are the days of just straight flushing. (Thank God). Today systems are organized into 3 types of Marine Sanitation Devices or “MSD’s”. The following explanation is from the US Coast Guard Website

canal poop
canal poop

Marine Toilets 

Approved MSDs: There are three different types of MSDs that can be certified by the U.S. Coast Guard to meet the requirements in 33 CFR Part 159, each having its own design, certification, and discharge criteria. For more information see 33 CFR 159.53.

  • Type I is a flow-through discharge device that produces an effluent having a fecal coliform bacteria count not greater than 1,000 per 100 milliliters and no visible floating solids. This type of device is typically a physical/chemical based system that relies on maceration and chlorination. Type I MSDs are issued a Certificate of Approval.
  • Type II is a flow-through discharge device that produces an effluent having a fecal coliform bacteria count not greater than 200 per 100 milliliters and suspended solids not greater than 150 milligrams per liter. This type of device is typically a biological or aerobic digestion based system. 
  • Type III is a device that prevents the overboard discharge of treated or untreated sewage or any waste derived from sewage. This type of device is typically a holding tank and may include other types of technology including incineration, re-circulation, and composting.

The Real Poop

What all this means is that for a houseboat toilet a Type III MSD is usually the system of choice. It consists of a head and a holding tank of suitable size. It will have to be pumped out at approved pump-out facilities or by portable collection boats. You have a fresh water tank, a gray water tank for sinks etc, and a black water tank for the nasty stuff. While it is possible to have a Type I marine toilet system that cleans and disinfects the waste, in reality, you cannot discharge it in the water. This is great for offshore, but most houseboats aren’t going out to sea.

A great website that explains all the systems in detail is Captain Rob Cozen’s newsletter on

If you follow the marine sewage news you will quickly realize that almost everywhere you go there are “No-Discharge-Zones” or NDZ’s. In fact, California has recently enacted laws to create the largest NDZ in the world. So, Either a Type III system that stores the waste or an expensive system that evaporates or incinerates the crap is the way to go.

If you are building your own little houseboat then a Type III houseboat toilet and tank is the best idea. Although you can still use a portable toilet if you want. It would be Ok for a day or two, but the joys of a week-long houseboat vacation might be ruined by the constant emptying of a twenty-pound tank of crap. (“just saying”)

Where does it all go?

When you flush a marine head the waste will go to a holding tank. Some marine toilets (or “heads”) have a garbage disposal-like device called a macerating pump. It runs on electricity and grinds the waste into a “slurry” (not to be confused with “Slurpee”) so that will not clog the tank or the pipes. But if you don’t have the electricity available you can install a “boat head” that you manually pump after using and it just flushes the waste into the tank. Then, when the tank is almost full, (don’t wait until it’s full ) you can pump it out at a pump-out station in a marina. In many marinas, they have a marine pump-out service available that periodically makes the rounds and empties your holding tank.

But remember, if it goes overboard you can be fined big-time. The government will swoop in and treat you and your marine toilet like a big toxic waste site. (which you would be) Return Home

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