Lessons We've Learned About Our Composting Toilet

 Updated June 22, 2020

Nearly two years ago, we installed an Airhead Composting marine toilet on our sailboat. We have lived on board full-time since then and have traveled several thousand miles. We don’t pretend to be experts, but we’ve learned a thing or two about this contraption.

The choice for a composting toilet was not something we rushed into. We seldom rush into any boat-based or life-based decisions, actually. Lucy and I tend to research things to death before picking. We both trend towards decision paralysis–impulsive is not our style.

Part of that mindset means that we’re also continually reevaluating our choices. So, how do we feel about our Airhead after constant use? What problems have we had? Hopefully, we can help others make informed decisions about composters.

How Does a Composting Toilet Work on a Boat?

A regular marine head works much like a home toilet. It takes water (usually seawater, but sometimes freshwater) and flushes the waste into a holding tank. In the United States, it is illegal to dump this waste overboard, so you must go to a dock with a pump-out facility to drain the tank. 

It sounds pretty simple, but in reality, there are a lot of moving parts. The hoses are small and wind through tight spaces in the boat. Every part of the system, from the seawater intake to the toilet to the hoses to the tank to the tank vent, can make a stinky mess when things go wrong. It is, in fact, a complex system of plumbing parts and biological reactions. 

A composting toilet for a boat or RV separates the liquids from the solids. It uses no outside water. The urine is diverted into a small holding tank that is easily emptied in a land side toilet. The solids get mixed with a composting medium (basically, clean dirt), and they dry out on their own. The solids tank is built-in under the seat, so there are no hoses or anything to get disgusting. You don’t flush a composting head. Instead, there is a handle that you crank, which churns the compost and helps break down the waste. 

Two big brand names are making composting toilet systems. They are very similar in functionality and price, so the choice comes down to which one fits in your boat’s bathroom the best. On Dulcinea, we have installed an Airhead composting toilet. The other brand is Nature’s Head. 

The Advantages of the Composting Toilet

Here are just a few advantages of a composting toilet over a standard marine system.

• There are fewer holes in your boat. A standard marine head usually requires two or three below-the-waterline through-hulls. A composting toilet requires none.
• There are no sewer hoses with marine heads. Hoses tend to absorb odors over time and need to be replaced (or at least cleaned out) every few years. Old sewer hoses stink, they are the leading cause of funky-boat syndrome.
• Since there are no hoses, there are no clogs. Regular marine heads clog all the time. Many boaters enforce “no toilet paper in the toilet” rules, but they still clog. Minerals from seawater and urine create a solid wall in the hoses over time until practically nothing can get through. 
• There is no joker valve. If you don’t know what a joker valve is, count yourself lucky. It’s a rubber flapper one-way valve that keeps the sewage in the hose and keeps it from back flowing into the toilet. When it fails (which they do regularly, every 6-8 months with full-time use), some fortunate person gets to disassemble the pump and hose connection and replace it. Is it easy? Yes, it’s pretty easy. Is it a clean, sanitary, and smell-free experience? No, it is most certainly not.
• The resultant product from a composter is far less disgusting than the raw sewage created by regular toilets. When it’s time to empty, you have a bottle of urine and some potting soil-like product.

 

Top Lessons Learned

1. Emptying a Composting Toilet Can Be a Pain, But Not the Way We Thought

One of the top reasons we got a composting toilet was so that we wouldn’t have to think about pump-outs. Our previous boat had two heads, each with a 20-gallon holding tank. A tank would last the two of us ten days or so, so we needed a pump-out about every 20 days. The tanks didn’t have gauges, so it was always hit or miss. It was better to be looking for a pump-out after 15 days.

The first challenge in emptying the composting toilet is dealing with the liquids tank. The Airhead came with one two-gallon jug that lasts us two days. So every other day, we need to have access to a shoreside toilet or be three miles offshore. That just isn’t going to happen.

I know a lot of users dump their liquids overboard. I’ve heard, “It’s just urine, which isn’t that bad.” Or, “Urine is sterile.” I don’t know about that, but I’m going to go out on a limb and say that pouring two gallons of pure human urine in the water is nasty, regardless of where or how it’s done. 

The one thing I do know–it’s illegal. A composting toilet may look different and smell different, but in the eyes and nose of the law, it is just another type of holding tank. And it’s illegal to dump a holding tank nearshore. For the record, if you used a Home Depot bucket, that would be a holding tank too!

The other problem with the liquids tank is that it is tough to keep clean. After one or two uses, it builds up a stinky funk like nothing else. It is the nastiest part of the composting toilet by far (Sterile? I think not!). It’s so funky that I have found myself deeply embarrassed after having funkified a marina bathroom’s air so badly. I started doing it in the night and leaving the exhaust fan running. 

And some marinas are on to us composters. We’ve seen more and more signs prohibiting dumping these tanks in the restroom. A few (and we mean we’ve seen one or two!) marinas have put in dedicated dumps for portapotties and composting toilets. Some even have composting piles! Hopefully, that becomes the norm.

We tried everything to get rid of the funk. We tried all the tricks online, including vinegar, urine digester, and holding tank treatments. Nothing did the trick easily. The only thing that we found works is to wash it out everything with a high-pressure hose and toilet brush. In all, that took 4-6 fills from the hose, so 12 gallons of water to do. And the hose needed to be much higher pressure than anything we have on board. Needless to say, this was a landside activity. We did it when we were in the boatyard, but there’s no way I’d be caught doing this on a marina dock. Yeesh.

We couldn’t live like this, and needing land access every two days completely defeats the purpose of a composter for us. In the end, we bought another one-gallon liquids tank and some hardware store plumbing fittings, including a simple gate valve. We plumbed the liquids tank into the boats holding tank. Our holding tank is low in the bilge, so gravity drains the small tank. This one change has made us over-the-moon happy with our composting toilet. 

Dulcinea has a 40-gallon holding tank, so the two of us can use the toilet for 40 days (!!!) between pump-outs. Because the composting toilet takes in no water, and it is only liquid going into the holding tank, there’s no risk of clogs or stinky hoses. We do add a bit of urine digester into the tank to help prevent mineral clogs.

2. It’s Not Compost

This one was a complete surprise to us. I mean, it says it in the name, right!? But if you read the Airhead user manual, it clearly states that if you want to use this compost in your garden, it should be first added to a separate compost pile to continue the process. And it should never be used for food crops. 

What these composting toilets actually do is dry things out to begin the composting process. The goal is to provide an environment appropriate for aerobic bacteria to thrive, but not for the stinky anaerobic ones. Technically, they are desiccating the waste, not composting it, but I guess that doesn’t have the same marketing ring.

The drying occurs on two fronts. First, the dry compost medium should absorb some moisture. The second is the exhaust fan, which should circulate enough air through the system to dry it all out in even the most humid places. We upgraded our fan to a more powerful one to help keep it dry in humid Florida.

If any liquid or soupiness gets in there, it’s time to empty the tank and start over immediately. We discovered that our toilet is mounted in a way that makes port tacks a problem. The toilet design means that it needs to be level (or even tipped a bit forward) to separate liquids from solids. On a port tack, ours lets liquid leak into the solids tank. The second that happens, you’ve got yourself some regular old raw sewage. Yuck. We’re working on a solution to this now.

3. Everyone Seems to Be Using Their Composting Toilets Differently

We figured this all out based on the great composting articles written by The Boat Galley. But this method of using the toilet seems contrary to what we read other people are doing, and even what the Airhead manual says. 

So what’s the right way? We don’t know; maybe they’re all right. But what we’re doing works for us.

Does the toilet paper go into composting toilets? According to the Airhead manual, it can. But again, this is preference. After years of dealing with stinky, clogging marine heads, we just put the paper in the trash bin. Since the Airhead instructions have you keeping the compost moist and leaving it there for a much longer time, I’m not sure that putting the paper in would work for us.

Another huge factor with the toilet is how much and how often it is used. We’ve found our system works great for just the two of us. I don’t know how well it would work with more people on board, and I don’t think I want to find out.

4. To Make It Work, There’s Some Trial and Error!

We’re delighted with our system now, but it took us about eight months to get there. If it hadn’t been for The Boat Galley articles, we would’ve been lost and unhappy. Here’s our basic process that we’ve settled on.

First, we make new compost. We use these 1.4 lb coconut coir bricks. I start by breaking it apart with a flathead screwdriver into the smallest bits that I can and put it all in a large two-gallon ziplock. Then I drizzle 1/2 cup of water over it all and seal the bag. I come back a few hours later and shake it up and break apart the remaining bits. 

A half-cup of water is the key because if you hydrate the coir per its instructions (remember, it’s sold to plant plants in!), then it’s far too wet. For our purposes, we need to break it apart but then let it get its moisture from the uhhh… “other things” we put in the toilet.

When the new coir is ready, we empty the toilet into a double plastic trash sack. I use gloves, and I have a dedicated toilet brush to get it all out. I know this sounds ridiculous, but it is not nasty, and the only odor is a slightly musky, dirt-like smell. I can say that because I’ve had regular marine sewer hoses, spew disgusting things at me and fill up entire bathrooms. Dealing with the compost product is easy. If it’s gotten wet, it’s a little icky and maybe a bit smelly. Still, it’s nothing compared to the things that come out of or go into a regular marine head daily. 

I used to clean the entire toilet religiously until it was spotless, but I’ve discovered that if the compost is kept dry, there’s nothing to clean. A quick brush out and maybe a wipe down with a paper towel takes no time at all.

The trash-sacked “compost” goes in the nearest trash dumpster. If I lived in the woods, maybe I’d think about starting a compost pile. But once that gets some moisture added to it again, it’s basically just a big ol’ pile of poop.

5. The Thing That No One Talks About Will Happen To You…Bugs!

Composting toilets are an open invitation for bugs, especially flies. The importance of rolling up the welcome mat and making it as hard as possible for them to access cannot be overstated. We hate flies. 

Our Airhead has very fine-mesh screens on all of the vents and super-secure rubber seals on both the lid and the seat. It’s very secure as long as those screens stay in place, but they should be inspected each time the compost is changed. The only time we had a fly problem was when the screen got pinched, allowing a small opening. 

The primary culprits are fungus flies, which look like fruit flies. They aren’t big black house flies, but they’re still pretty darn annoying. There are many online remedies available. We used diatomaceous earth for a while, but we found it a pain to use. The fine powder also seemed to clog up the bug screens faster and restrict airflow. We stopped using it and haven’t had any problems. Just make sure the screens are intact! 

See one or two flies in your head? Empty the compost and scrub every inch of the toilet, with bleach or boiling water. The eggs are there, and they’re probably in the nooks and crannies. If you can take the tank and lid assembly to a powerful garden hose, that’s a good idea. Clean, clean, clean. Then inspect the screens again and start with fresh compost. 

6. The $1,000 Plastic Bucket

So, is the Airhead just a $1,000 plastic bucket? A lot of DIY composting toilets are out there, and it seems like an easy project. But we appreciate the design that has gone into this toilet for a lot of reasons. A lot of thought went into getting it to separate liquids and solids. And a lot of thought went into keeping bugs out. They’re built out of sturdy roto-molded plastic, and they’re pretty compact for what they are.

Many folks opt for building a DIY marine composting toilet, or they try the C-Head. These are much simpler and less expensive systems. In our opinion, they aren’t in the same class as the Airhead and Nature’s Head. We can’t say for sure since we haven’t used them, but they seem to lack some essential features found on the two listed above. Some don’t even have vent fans to circulate the air, so I have serious questions about that since I’ve had to upgrade my fan to promote drying.

For us, buying the Airhead was a small price in our overall refit budget. We’re happy with the system and its design, and when we see pictures of C-Heads and DIY systems, we think we made a great choice. But your mileage may vary.

Bonus Tip–Add Some Light

One of the problems we had with our toilet was seeing when the liquids jar was nearly full. There's no overflow protection here...if you miss that the bottle is full it will wind up on the floor. It has a viewing window, but in our dimly lit head it was impossible to see. We started using a flashlight, which worked okay. Then one day, I stumbled on these motion-activated toilet lights. I wedged the LED between the liquid and solids tank and mounted the battery box and sensor on the side of the liquids tank. Now it lights up when you enter the head. Voila! Now we can see the fluid level clearly. 

Conclusion

Now that we’ve moved past the trial and error learning phase, we love our composting toilet. It has far fewer odor problems than any other marine head we’ve ever owned. We have zero odors unless something has gone wrong (liquid in the solids). With the liquids tank draining to the holding tank, we can go 30-40 days between pump-outs. We change the compost every 3-4 weeks. It is trouble-free and easy to use. 

If your boat has two heads, we think the perfect solution would be to have a regular marine head and a composting head. Then you’d have the best (and worst) of both worlds…a composting head for your daily use, and a regular head for when more people are on board, or when getting access to pump-outs is no issue. 

We also think that plumbing your composting head’s liquid tank to the boat’s holding tank and pump-out fitting is essential. Our style of cruising just does not suit finding shore access every two days to empty the liquid tank.

Being the researching and fact-finding souls that we are, we both find that getting the truthiness out of the internet is the hardest part of boat projects. Composting toilet questions pop up online regularly, and they are always beset with a tirade of positive and negative comments. Most of the commenters, in our experience, have to be ignored if you want an honest assessment. There are too many fanboys (and girls) who leave out the bad bits. And there are too many nay-sayers who just don’t know what they’re talking about. Oh, the internet–we love you.

The ugly truth is that both composters and regular marine toilets suck in their own ways. Dealing with sewage safely and responsibly on a boat sucks. You can learn to manage any kind of system safely and responsibly if they are high-quality and installed well. But to figure out which one you want to use, you need to know the truth about each one. Hopefully, our experiences can help you make a sound decision for your crew.