Best Marine Composting Toilet – Options and Opinions

Published Categorized as Boats

Collect any group of boaters, and what do you think they’ll talk about? Anchors? Sail trim? Religion? Politics? Maybe eventually, but one topic comes up before all others – marine toilets.

In honor of this age-old cruising tradition, here’s an entire article on my marine composting toilet. After three years of battle with two traditional head systems in my last vessel, I installed a composting head when I purchased my current boat. Four years on, I have regrets.

The one thing I’m now certain of is that composting heads are not all they are cracked up to be. They have many ardent supporters, but in daily use, mine disappoints me.

Here’s a look at the most popular models, plus the benefits and disadvantages I have found during my experience with one.

Table of Contents

marine composting toilet

Best Marine Composting Toilets

There are only two widely-available composting toilets that are small enough to be suitable for boat or RV use–the Air Head and the Nature’s Head.

They are nearly identical. The only way to differentiate between them is their shape and size, so the one that is right for you is the one that fits best in your boat.

Nature's Head Self Contained Composting Toilet with Close Quarters Spider Handle Design
Prices pulled from the Amazon Product Advertising API on:

Air Head Composting Toilet

For the last four years, I’ve used the Air Head toilet full-time, living on a sailboat, so I’m beginning to figure it out. Unfortunately, I have a lot of problems with it. It has just taken me four years to accept that they are problems, not operator errors.

The Air Head is comprised of three parts–the upper unit with the lid and seat, the liquids tank, and the solids tank (aka the compost bin). They lock together with set screws and gaskets. All are made from rotomolded polyethylene plastic, the same material that plastic kayaks are made from.

The seat comes in two sizes, household or marine. The seat and the lid have gaskets to ensure no bugs can enter the solids chamber. It’s really important to keep the lid down when not in use!

The lid also attaches to an air hose that vents outside. A 12-volt fan pulls air out of the toilet and exits through a deck vent, which you’ll have to add. This might mean cutting a three or four-inch hole in your deck, although many people repurpose a deck fill. The vent line includes a bug screen and fan housing.

The solids tank comes in two shapes, one with a flat back and one with a cutaway hull shape. The tank has a stainless steel auger connected to a handle on the left or right side. We find that the solids tank lasts about three weeks in our conditions (one couple living on board full time).

Finally, the liquid bottle fits under the front lip of the lid on its own mounts. You can choose a one or two-gallon bottle. The two-gallon tank lasts the two of us two days.

Air Head sells all of the spare parts you might need on its website. They also sell a liquids tank with a holding tank fitting, a recommended accessory if you can make it work in your boat.

Nature’s Head Composting Toilet

There are only two big differences between the Air Head and the Nature’s Head. The Nature’s Head has the same three units, but the top includes a seat and frame that the tanks sit inside. To remove the liquid tank, lift the seat assembly and pull the tank out from the top. You can remove the liquid tank on the Air Head without moving anything else.

The second difference is that the Nature’s Head’s frame means it’s a little larger. The difference is slight, but most marine installations are tight on space. Again, the unit you choose has everything to do with how and where you’re installing it. Triple-check your measurements!

While I haven’t personally used the Nature’s Head, I know many folks with one. The best review is from Carolyn Shearlock of The Boat Galley. https://theboatgalley.com/our-composting-toilet/ Shearlock has had many of the same problems we have, and her articles were a great help to us as we worked through them.

Other Composting Toilets

C-Head

C-Head was a competitor for many years but appears to have gone out of business. The C-Head was smaller and simpler than the other two.

Many people use the C-Head with good luck, but it is much more rudimentary than the two mentioned above. It uses standard one-gallon water bottles for the liquids container and requires the user to be good at aiming to ensure the solids stay dry.

Separett Villa 9215

The Separett is a Swedish-made competitor. Its specifications appeal to the boater, even though it’s not specifically designed for mobile installations. The fan will work on either 12 or 120-volt power.

This is simply a dry toilet that bags the waste. You do not need to use a medium like coconut coir; solids are collected in a bag for easy disposal. You can then add them to your composting pile if you have one. There is also no liquid tank. Therefore, this option is only good if you can plumb it into a traditional holding tank.

Overall, this toilet is a bit simpler in concept than the Air Head and Nature’s Head, which might be a winning combination.

OGO Composting Toilets

The OGO is a new competitor to the Air Head and Nature’s Head in the US. Its primary upgrade is that its agitator is powered, so there is no cranking. That means it uses more power, but the agitator is on a 45-second timer and only adds 1.8 amps to your daily usage. Ditching the manual agitator enables OGO to make the toilet much more compact.

The OGO also has a light to indicate that the urine bottle is full, a welcome feature. And the urine diverter looks more effective than other options.

How Does A Marine Composting Toilet Work? The Thing Everyone Gets Wrong

Composting toilets do not compost anything. It’s a marketing phrase they use because the word “desiccate” isn’t as appealing.

What’s the difference? Composting is the breaking down of organic matter, usually food waste or manure. Many people know of composting from gardening, where compost material is added to soil as a plant fertilizer.

Correctly composting human waste is a multi-step decomposition process that takes six to twelve months. It needs aeration, fungi, worms, and other detritivores help break up the materials, and aerobic bacteria help convert it. It requires equal parts of carbon, nitrogen, oxygen, and just enough water.

This isn’t even close to what marine composting toilets do. They are too small, with inadequate airflow, and only one material (human waste) added to the medium.

These toilets desiccate the waste, which simply means they dry or dehydrate it. As used on a boat, a composting toilet separates liquid from solid waste to keep the solids dry. That’s it.

Some sailors I know refer to composting heads as “litter boxes.” They aren’t wrong.

Once the liquid tank is full, you must empty it in a toilet on shore. Once the solids tank is full, the only thing most boaters can realistically do is bag it and throw it in the trash dumpster. It’s not compost, and most boat owners have no way to add it to a compost pile.

If you did want to make compost, you’d have to add it to a bigger compost pile outdoors with other compostable materials. Even still, it’s never considered safe for use on edible crops.

Nature's Head Self Contained Composting Toilet with Close Quarters Spider Handle Design

The Law and Composting Toilets – The Other Thing Everyone Gets Wrong

You need to be aware of two sets of laws and regulations when considering toilets on boats.

The first is the toilet itself. Toilets on boats are called MSDs (marine sanitation devices) by the Coast Guard. Nearly all recreational vessels have Type III MSDs, which hold untreated waste onboard to be removed at shore-side facilities. If it has an overboard discharge, it must be locked to ensure it can never accidentally be opened.

The Coast Guard does not certify or approve Type III MSDs. Therefore, an MSD can only be said to meet the above standards.

The most common Type III MSD is a standard marine toilet connected to a holding tank. But the rule doesn’t care how you hold the waste or what the waste is. It must be held in a container on the boat and emptied on shore. For example, a five-gallon bucket could be a Type III MSD. Porta-potties are Type III MSDs, and so are composting toilets.

The second set of rules you need to know is the no-discharge zone laws. These are set by numerous governmental agencies, from the Coast Guard and Environmental Protection Agency to local county or city governments.

But we can keep it pretty simple. In most places, it is illegal to dump any waste overboard within three miles of shore. In some places, you have to go much farther out to sea than that.

To be clear, the rules do not differentiate between liquid and solid waste. If the waste is held onboard, it cannot be discharged overboard legally unless you are well offshore.

Plenty of folks will tell you that urine doesn’t count, that it’s sterile and doesn’t harm the environment. Unfortunately, that’s not true–urine is high in nitrogen and a powerful fertilizer that causes algae blooms. But whether or not you believe it’s harmful, it’s still illegal to dump it.

In Marathon, Florida, the city requires proof of pump outs. Composting head owners must prove they dump their tank ashore, and the city has kindly provided facilities to do so.

In 2018, the harbormaster in Annapolis, Maryland, banned composting toilets on boats staying on a mooring or at anchor for more than one week. Worse, no accommodation has been made for visitors with no other option.

This issue isn’t talked about enough. Unfortunately, this will become a bigger problem for composting head owners in the future, and local regulations are always in flux.

are composting toilets legal?

Benefits of Marine Composting Toilets

With all of this in mind, the benefits of a composting toilet begin to wane. But the truth is that many standard marine head installations are so bad that even a composting head is a better option sometimes. When you’re shopping for great sailboats to live in, the toilet seldom gets a second thought. But it should!

Here are a few benefits of having a composting head onboard.

Sidenote: One benefit you won’t see on my list is smell, or lack of it. This is because a boat toilet–whether composting or not–should not smell. If your boat has a “boat smell,” just putting in a composting toilet isn’t enough to fix the problem. It’s possible to have a standard marine toilet with less smell than a composting head.

Simpler and Easier to Troubleshoot

In many ways, the composting toilet is a $1,000 bucket. There’s no plumbing to speak of, no pumps, no valves, no hoses. And with this in mind, it’s impossible to stop up the plumbing.

Keeps Waste in a Less Vile Form

Can we all agree that nothing is grosser than raw sewage? While the composting toilet forces you to deal with waste directly, the fact that it separates wet from dry helps. There is usually very little smell, so it isn’t that gross. It’s unpleasant but not quite gross.

Go Longer Without Pump Outs/Servicing

If you have a two-gallon liquid tank, it will last about two days. So you’ll need a way to empty it, in a shore toilet or a larger holding tank.

In my opinion, a composting head is best combined with a holding tank and its associated plumbing. This gives you a 20 or 30-gallon liquid tank, which you can pump out at the marina. We do this, and we can go six weeks between pump outs (living onboard full time). Remember, there’s no flushing water with a composting head, so the holding tank will last a long time!

Fewer Holes in your Boat

A composting toilet does not need any through hull fittings below the waterline. Standard toilet systems usually have two (sometimes three) per toilet–one to bring in seawater to flush and one to discharge the holding tank when offshore.

But most boats already have the holes, and few people bother to fill them. Properly filling a through-hull is a major undertaking in the boatyard, both in terms of money and time.

Disadvantages of Composting Toilets

Life with a composting toilet is not all sunsets and cocktails, however. While they aren’t as troublesome, they still cause trouble.

Larger and Taller than Regular Boat Toilets

Getting the composting toilet to fit in your bathroom is just the first problem. Then, you must figure out if it’s too tall to sit on. While it may be serviceable, it’s awkward when at sea.

In other words, they are clumsy to install and use on a boat. Yes, they can fit. But they are far from perfect.

Getting Compost Medium

You can order dehydrated coconut coir on Amazon and occasionally find it at hardware stores and gardening centers.

But if you’re spending a few months in The Bahamas or any other remote cruising destination, you’d better bring enough with you. Coir isn’t very expensive, but it is one more thing you’ll have to plan for, provision, and order in advance.

Harder to Clean

Both the design of these toilets and the plastic material are difficult to clean. The Air Head and Nature’s Head are made from porous, soft rotomolded plastic. Newer designs like the OGO might be better. Either way, these are not typical sailing materials that stand up to heavy use.

Specifically, the underside of the lid area of the Air Head and Nature’s Head are a mess of nooks and crannies. To clean it, we use a hose sprayer and a long brush. But you still can’t get to it all, especially around the urine diverter.

Diverter Doesn’t Always Work

The Air Head and Nature’s Head have a built-in funnel shape that keeps the liquids flowing in the right direction. But the toilet needs to be perfectly level. At sea, the urine diverter will inevitably fail as the boat moves around. And neither designs work well for men standing up–both companies recommend that men always sit.

As soon as a little urine goes into the solids tank, you have raw sewage. Yuck.

Bugs!

We have been plagued by bugs countless times. They are always the same small fungus flies that look like fruit flies. By the time you spot one, you’ve got an infestation. This has happened repeatedly, despite all troubleshooting and pesticides, year after year.

We have also noticed that the deck vent attracts swarms of black flies, but luckily they can’t get in. Yuck.

Smells

Composting toilet makers want you to believe that they are smell-free. This is not the case. The urine bottle is the worst; it can get extremely smelly. It can get so smelly that emptying it in a marina bathroom funks up the whole room.

We’ve been at a handful of marinas that now have “no composting toilet or porta-potty tanks” signs on their bathrooms. But, on the other hand, we’ve also stayed at a few that have convenient outdoor dump stations set up for them.

The solids tank is usually fine unless it gets too much moisture. Then it smells like…well, poop. A lot of poop.

Cleaning the Litter Box

And then, there’s the monthly chore of cleaning out the solids tank (or more often if you get bugs or a liquid leak). There’s no way to do it without gloves. And the idea that you don’t need to deep clean it with chemicals? That just encourages the bugs to keep coming.

Oh, and all those videos of folks neatly dumping it into a trash bag? Isn’t it funny how they’re all shot in a wide-open space (not inside a cramped boat) and with an empty solids bucket? Somehow, they never make a mess. Amazing!

Carrying Around Jugs of Pee and Bags of Poop

How do you feel about walking into the marina bathroom with two gallons of your smelly pee? I don’t like it, but that’s me. How do you feel about walking to the dumpster with 15 pounds of your poop? I don’t like that either. But perhaps I’m weird?

Pump-outs don’t bother me as much. A pump out is always more pleasant than cleaning the solids tank after a fly infestation, even when there’s some accidental leakage or a momentary smell.

Is a Composting Toilet Right for Your Boat?

If it’s not already obvious, I’ll lay my cards on the table. My next boat will have a conventional marine head. I will rebuild the system myself, ensuring everything works right.

When you compare owning and using a composting head to a poorly installed and badly maintained conventional system, the composting head is better. And honestly, there are so many terrible boat toilets out there (especially when you look at cheap boats for beginners) that this is where the market is.

But when you compare a composting toilet to a properly installed and designed conventional system, the standard toilet wins every time. And most owners can get their systems working fine for the same money or less than a composting toilet.

A great resource for learning about the design, care, and use of marine sanitation systems is the excellent book by Peggy Hall, Get Rid of Boat Odors: A Boat Owner’s Guide to Marine Sanitation Systems. It includes some great information on composting toilets.

Here’s one final thought from my years of boat ownership. All marine toilets can have problems, and there’s no magic bullet solution. Composting toilets solve problems for many people and check the right boxes. For me, the problems with the composting toilet are worse than those with a regular head.

Marine Composting Toilet FAQs

How does a marine composting toilet work?

A marine composting toilet works by separating the liquid from the solid waste and containing each in separate containers. The waste is dried and mixed with a soil medium like coconut coir or peat moss. Assuming everyday use, you’ll have to empty the solids every three or four weeks. The urine is stored in a jug and emptied in an onshore toilet every few days.

Can you put a composting toilet on a boat?

Yes, a composting toilet can meet the Coast Guard regulations as a Type III MSD (marine sanitation device) as long as it does not allow the waste to be discharged overboard.

Do marine composting toilets smell?

Yes and no. Composting toilets, when operating correctly, have very little smell. The urine tank is usually the smelliest part. The solids tank should smell a little earthy, like peat moss. But if the solids get too much moisture, they will smell like sewage.

Are composting toilets USCG approved?

Yes and no. The Coast Guard does not “approve” Type III MSDs; it just says they cannot discharge waste overboard. So, you can use a composting toilet and be legal, as long as you do not dump any waste in the water.

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