The best marine composting toilets for your boat - header image

Considering a marine composting toilet? This guide will help you decide if a composting toilet is right for you, and help you choose the best one for your boat.

Imagine watching the sunset in a beautiful, secluded anchorage, drink in hand, and not a care in the world.

Until nature calls and you realize that your holding tank is full and there’s not a pumpout in sight.

[Cue the record scratch]

Where and how you go to the bathroom isn’t often talked about openly — in normal circles anyway. But for boaters, it’s a hot topic, often discussed casually over cocktails.

One of the biggest boat head discussions? Regular marine toilets vs. marine composting toilets.


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The 3 main types of boat toilets

Before we get into the details of a composting toilet, let’s quickly talk about the 3 main types of toilet (head) options you have for a boat and what the difference is.

1. Manual Head or Pump-Out

This is probably what most people think of when they think of a boat toilet. It basically consists of a toilet which you pump into a holding tank or directly overboard (if offshore… know your local regulations).

You empty the holding tank at a marina pumpout station or 3 miles offshore (if your plumbing is configured to empty your tank overboard.)

These can be manual flush or electric flush, which are pricier, but may be worth the convenience, although you won’t get the nice arm workout.

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2. Cassette Toilet or Portable Marine Toilet

This “porta potty” type of toilet is more common in RVs or weekend boats. Basically it’s a stationary toilet with a portable holding tank which you can carry off the boat and empty into a marina toilet when you arrive. Chemical additives help break down the waste and keep the smell down.

Some boaters like these because they’re affordable, most costing less than $150. One popular brand is the PortaPotti.

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3. Composting Toilet

A composting toilet is a “dry” toilet that breaks down waste via microorganisms through a natural process called composting. These toilets separate the solids from the liquids, then use a dry organic material such as sawdust, coconut husks, peat moss to dry out the solids allowing them to break down more quickly.

What’s that smell?

Now, if you’re a liveaboard or have spent any time on a sailboat or in an RV, then you know the smell. Most sailors call it boat smell. I call it nasty (and unnecessary).

Most boat toilets these days involve some sort of holding tank or black-water tank which contains both liquid and solid waste. It’s usually stored below a bunk somewhere on board and… it usually smells.

Doesn’t matter how many times you clean your toilet or what you use. The simple act of flushing the toilet with raw water (ocean, lake, or river) introduces organic matter (plankton, plant life, fish, etc.) into the system where it decomposes and–you guessed it, smells like… you know what.

If you haven’t smelled it before, the best way I can describe it is a musty, mild fishy sewage smell. That’s one of the reasons many boaters are making the switch to composting toilets. That means no incoming water. No holding tank. No smell.

How a composting toilet works

Here’s a quick breakdown of how a marine composting toilet works.

Composting toilets separate the liquid waste (pee) from the solids (poo), by diverting each one into its own container.

You add dry, organic material such as coconut fiber or peat moss to the solid waste bin to mix with and promote the composting process. An agitator bar stirs the mixture and a small fan accelerates the dehydration process.

Keeping the liquid waste separate from the solid waste does two things:

  • It virtually eliminates odors. Because the solids and liquids don’t mix, you won’t have the nasty sewage smell.
  • Having the liquid and solids in separate compartments makes handling the waste easier and, dare I say, cleaner. But we’ll get into that a bit later in the pros and cons section.

How to dispose of your composting toilet waste

Now, let’s answer that burning question: What do you do with the doo? 

You have to empty it yourself.

How often you need to dispose of your composting waste depends on the number of people using it, how often they go, and the tank size.

According to Nature’s Head, a leading composting toilet brand:

“The toilet is designed for 1 to 4 people full-time. Generally, two people full-time people’s usage will require emptying approximately every 3 weeks; additional people will shorten the time. If using just on weekends with 2 people, that can extend time to 2 months or more. The urine bottle holds 2.2 gallons and requires more frequent emptying; two people might need to empty after 3 days.”

Maybe you’re thinking, “I’m sorry, I just don’t want to see my poop every 3 weeks.”

This is the big knock on marine composting toilets. People don’t want to mess with poo.

But… let’s look at what interactions we have already with conventional holding tank toilets.

Have you ever:

  • Pumped out your holding tank and had the suction device fail, spraying you in wet, nasty sewage?
  • Inadvertently over-filled the tank and had sewage seeping out pressurised vent hoses?
  • Had an unknowing crew member forget and clog the system with toilet paper or femine products?
  • Had to replace a toilet, hose, or faulty y-valve?

Unfortunately, I can answer yes to all of the above, and it’s downright disgusting.

Here’s the thing: If you live on a boat, at some point you’re going to have to interact with your toilet waste.

Why you might want a marine composting toilet

  • Ease of use: Right off the bat, the marine composting toilet is game changer for easy set-up. Theres no plumbing, no valves, no holding tanks, and no thru hulls. You simply bolt it down, run some basic electrical wiring to power the fan, and run a vent hose.
  • Eco-friendly: For some, like us, this is extremely important. Marine composting toilets use no water and no harsh chemicals, and the composting process is all natural.
  • It’s more sanitary: Another biggie for us. After cruising for nearly a decade, we grew tired of pumping out the holding tank and changing rancid hoses. We’d much prefer to carry a sealed container of urine or bag up a bunch of dry organic material. This is much easier and to me, much cleaner.
  • No accidental discharge: This is something I rarely see addressed when people discuss marine toilets. The laws surrounding illegal discharge of waste are stringent and fines are substantial. All US inland waterways and rivers are designated as No Discharge Zones. This means if you accidentally pump overboard in one of these areas and get caught, the fines could be disastrous to your cruising kitty. Not to mention your mariner credentials if you’re a licensed captain. Composting toilets eliminate the possibility of accidental waste discharge.
  • Space Savings: Do away with the 25-gallon black-water tank under the v-berth and you’ve just created a bunch of space for another fresh-water tank, additional battery storage, or a parking spot for the air-conditioner you always wanted.

But it’s not all sunshine and daisies. Let’s look at the cons.

Why you may not want a composting toilet

  • Price: There’s no way to sugarcoat it. These fancy poop machines are expensive. The top-selling Nature’s Head sells for around a thousand dollars. When you consider that a Jabsco manual pump toilet sells for around $200, it’s easy to understand how cost could affect your desire to switch to a head of the composting variety.
  • Handling and disposing the waste: This is another big knock against having a marine composting toilet on board. You physically have to empty the unit and this puts you up close and personal with your pee and poo.
    And if you’re not sailing solo, you’ll be up close and personal with someone else’s poo, too. A dealbreaker indeed for those poo-averse folks.You also need to dispose of the waste properly. The most responsible thing is to dump urine straight into a marina toilet. You can bag the solid waste (in compostable bags, of course) and toss it in a dumpster or into a compost bin.
  • Aesthetics: They aren’t the prettiest things on the planet. Most are made of molded plastic, and while that makes total sense for cleanability, it doesn’t do much to bolster their “curb appeal.” In fact, the Nature’s Head has an odd-shaped, molded toilet seat that is a turn-off for some. While some companies are now leaning towards a more fashionable loo, they come at a cost.

Okay, we’ve covered the what, the why, and the why not. Now let’s get to the nitty-gritty.

5 Best Marine Composting Toilets

1. Air Head Composting Toilet

The Air Head is our top pick. It’s similar to other composting toilets in overall design, but has two unique differences that I think are worth noting.

First, the seat is not molded to the unit like other designs. It looks more like a regular toilet seat in that it’s round, and it can be removed and replaced. The entire unit has a round shape that may fit better in tighter spaces.

There’s also a marine version seat that’s smaller (again, saving space), and you can get a hull-shaped tank which could be ideal for smaller boats.

It’s also made in the U.S.A and comes with a 5-year warranty.

The best marine composting toilets for your boat - air head composting toilet dimensions

Manufacturer specs:

  • Item Dimensions (L x W x H):  15.5 x 19 x 19.5 inches (w/small urine tank)
  • Weight: 19 Pounds
  • Liquid Bottle Size: 1 gallon or 2 gallon option

What we like:

  • Comfortable toilet seat
  • Round shape makes it easier to fit in small spaces
  • Has option for hull-shape tank or flat back tank
  • Opaque urine container for better visibility

What we don’t like:

  • It’s pricey
  • Current 12-week lead time (as of this posting) due to COVID-19

2. Nature’s Head

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This toilet is one of the top sellers for a reason. It just works.

It’s made in the U.S.A, features all stainless steel hardware, and has over 50 distribution centers worldwide. So if you’re sailing to remote locations and have a problem, chances are good you’ll be able to get what you need.

Their customer service is highly rated and the toilet comes with a 5-year warranty.

Manufacturer specs:

  • Item Dimensions (L x W x H):  22 x 20.5 x 21.7 inches
  • Weight: 28 Pounds
  • Liquid Bottle Size: 2.2 gallons

What we like:

  • Proven brand
  • Parts are readily available
  • Easy installation

What we don’t like:

  • Molded seat
  • Not always easy to see how much urine is in container
  • Must open the solids compartment to retrieve and empty the urine container
  • Small opening for solids to pass through so it can become messy
  • Fan may not be adequate

3. Separett Tiny® with Urine Container

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This one is a unique beast. First of all, it’s not really a composting toilet, but a urine diverter. So while it does separate the liquids from the solids, it does not require you to add organic material to the solids bin. No coconut fiber or peat moss.

Separett provides you with compostable bags instead. They believe that the fan alone dehydrates the solids sufficiently enough provided the amount of time they’ll be in the container. Another nice feature is the sensor that illuminates red when the urine container is almost full.

It’s an innovative approach wrapped in their latest, sleek design.

Manufacturer specs:

  • Item Dimensions (L x W x H):  20 x 16 x 19 inches
  • Weight: 19 Pounds
  • Liquid Bottle Size: 1.8 gallons

What we like:

  • More modern design
  • Compostable disposal bags

What we don’t like:

  • It’s pricey
  • It’s a new product, so there aren’t a lot of substantial reviews

4. Sun-Mar GTG Toilet

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Like the Separett, this is another sleeker design that’s not as big as the more popular Sun-Mar toilets. It’s also easy to install. You can use a composting medium such as “compost magic” from Sun-Mar to compost the solid waste.

Manufacturer specs:

  • Item Dimensions (L x W x H):  24 x 15.75 x 19.8 inches
  • Weight: 29.5 Pounds
  • Liquid Bottle Size: 1.85 gallons

What we like:

  • Modern, utilitarian design
  • Easy installation
  • Sturdy materials
  • Easy to remove seat for cleaning

What we don’t like:

  • No trap door so it’s easy for urine to get mixed in the solid tank
  • No crank handle to mix solids and dry material
  • Oblong design takes up more room

5. C-Head Composting Toilet (Budget Pick)

The best marine composting toilets for your boat - c-head composting toilet

If you’re looking for the most basic setup you can get, the C-Head might be right for you. It’s a true urine-diverting composting toilet without all the bells and whistles.

There’s no fan requiring electrical wiring and no vent hose to run through the boat. It also comes in customizable finishes and sizes.

Manufacturer specs:

  • Item Dimensions (L x W x H):  20 x 15.25 x 18 inches
  • Weight: 29.5 Pounds
  • Liquid Bottle Size: 1.85 gallons

What we like:

  • More affordable than the other marine composting heads
  • Small company with direct interactions with their customers

What we don’t like:

  • It’s still pretty pricey for what it is
  • Not a fan of the design


If you’re a liveaboard or cruising sailor fed up with the head smell permeating everything from your clothes to your bedding, the marine composting toilet is an option to consider.

Are they perfect? No. But they solve a lot problems for sailors like us who are simply tired of the battle with the bowl. No amounts of white vinegar or Unique Marine Digest-it could ever completely eradicate the boat smell we’ve all fooled ourselves into ignoring.

Another plus is the eco-friendly component. Mother Nature needs all the help she can get these days. Considering the ever-intensifying pressures on the environment, changing to a product that allows us to move along with a smaller footprint was a no-brainer.

I do believe with each new iteration, composting toilets will improve and the costs will come down.

Whether or not you choose a marine composting for your boat, you now know what the most popular models offer, and can make a more informed decision about your choice.

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