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Composting Toilet – How it works

Nature’s Head

What about the poop? Everyone wants to know how we could possibly use a toilet that doesn’t flush and doesn’t use water. And how can it NOT smell?  Most of this text is from the Nature’s Head, Incinolet and  Sun-Mar websites since they are thorough and easy to follow.

We are using the Nature’s Head composting toilet.  Nature’s Head, Incinolet and Sun-Mar each make a composting toilet that will work in an RV application.  For us to make the right decision we needed to compare things like size, weight and price of each model.  In the RV, you have to carry everything you need with you, including your water.  We saw using a composting toilet as an opportunity to use less water, increasing our ability to stay off the grid and boondock as well as an excellent way to reduce our need for a precious and dwindling resource, water.  At first we wanted to use the Sun-Mar toilet because it evaporated urine (and we were uneasy about emptying the urine container on the Nature’s Head unit).  But after considering several factors, (having to completely change our bathroom floor plan was the big one) we decided that the Nature’s Head unit was the best choice for our application.

In the Nature’s Head unit, the liquids are not mixed with the solid wastes and you get an exceptional amount of uses before you need to empty the unit. For example; a couple using their boat or cabin on the weekends may go an entire summer without having to empty the solid’s tank.  We will be using it every day so we empty the solids about every 1.5 – 2 months. The front liquid tank is approximately 2.2 gallons and will need to be emptied more frequently – about twice per week. Check local regs. to know where and how you can dispose of urine.  Many gardener’s water down urine and add it to their gardens (click here for Mother Earth News article). Collecting and disposing of urine was the trade off with using the Nature’s Head versus Sun-Mar and Incinolet.  The others evaporate the urine using electricity.  However, both units are much bigger in size and would not fit into our RV bathroom unless we reconfigured the floor layout.  The existing RV toilet dimensions were H-12.5 inches, W-14 inches and D-18 inches.  The Nature’s Head unit is H-20, W-13 and D-17.  The Sun-Mar mobile unit is H-30, W-19.5 and D-23.  The Incinolet RV model is H-20, W-15, D-24.  Weight was also an issue – Nature’s Head weighs 28 pounds, Sun-Mar 40 pounds and the Incinolet 100 pounds.  The price was the last factor – NH was around $850, Sun-Mar mobile unit around $1550 and the Incinolet RV unit around $1700.  In the end, you have to look at all the factors and decide what is right for you.

In the  Nature’s Head composting toilet, the toilet separates the liquids from the solids (to put it politely) – it doesn’t smell bad. It’s when you mix the urine and the solids that you get the really bad odors associated with sewage. When working properly the toilet will have a slight earthy smell when you open it. The vent to the roof allows moisture to escape. The resulting compost is a valuable resource which is ideally suited for uptake by plants, and goes from a composition of roughly 70% water down to 10%.  This is truly a breakthrough and shouldn’t be overlooked as a viable waterless toilet alternative.

The Nature’s Head unit also contains a lock that ensures that the composting drum is held upright under road conditions. The toilet is very economical to operate; there are NO chemicals to buy.   Throw in a little bit of peat moss or be even more sustainable and use coconut coir.  Throw in a little coir, crank the handle, spray down with a vinegar solution every once in a while and you’re done.



Sun Mar Mobile


  1. 4o years ago I imported a compost-toilet from Sweden. My house Canalisation wasn’t ready. I can well remember for example during a party with many WC users, that I had to give milk powder and freshly cut grass in the bowl…..

  2. I and my beloved will travel in our first trailer this summer. A 1986, 26 foot Playmor is our first rig. Definitely want to be green as possible especially to eliminate the blackwater issue and use lots less water all around. I’m looking at the Natures Head model for size, weight, portability and of course, cost. MY QUESTIONS: What difficulties might I encounter in removing the old toilet? What probs might I encounter with the workmanship of the Natures Head? Who might i contact with questions concerning the vent on the NH and how to connect it to the stock Playmor toilet vent system. . . or will I need a whole new venting system entirely? Thank you very much for your assistance. jerry

    • Thanks for contacting us at On the Green Road. I would love to share our process with the composting toilet so far.

      First congrats on the trailer! We looked at all the composting toilet options and also decided to go with NH for weight, size and price. It will was just delivered and we are in the process of putting it in. It was super easy for us to remove our existing Rv toilet. Several brackets to remove and it lifted off it’s seal/gasket. We covered the open hole with a bag and tied it off. We later removed the black water tank all together since we won’t need it. We had to drill though rivets on the underside on the airstream and remove the sheet/underbelly. From there just several brackets to remove and the black water tank could be pulled out. We are going to divert rain water from the roof through a UV filter system and into the existing fresh water tank. Super green and efficient this way. When you get the NH toilet there are 2 brackets to use to drill the toilet into the floor and a flexible hose pipe connects to the existing venting. We will put more info. on our site as we use it. Thanks again for your ?? and good luck with your journey!

  3. Hey you 2. Very cool project, just wanted to drop a line and say hello. Can’t wait to hear more about how the toilet holds up over the years. Cheers.

  4. I have installed a Sunmar Mobile, and am not very happy with it. I still prefer it to having a holding tank since I dry camp a lot, but it is poorly made and the liquids never seem to evaporate so I stopped peeing in it. I had one tooth on the gear that rotates the drum break off after a few months of use and emailed the company and phoned and followed up a few times and never got any results. I want to buy a NH, but after spending $1600 on my sun-mar. I am feeling cautious about buying a NH without doing a bit more research. Could you give us an update? Thanks,

  5. Hi James – Good to hear from you but not good to hear about your toilet experience. We were hoping when we settled down that we would use one of the Sun Mar toilets (not the mobile one) as our household toilet. We have been full-timing for close to 8 months now using the toilet daily. The Nature’s Head has been good for our specific needs. Only uses 1 amp of energy and is the smallest, cheapest and lightest of the composting toilets. That is what sold us in the first place. For the most part the toilet has been great. It separates the pee and poo so you have to empty the pee every few days. That’s the biggest hassle and can be a smelly mess. Otherwise the composting part of the toilet is easy and doesn’t smell. It gets emptied every few months and all it contains is poo, toilet paper and peat moss. We wouldn’t want to use a Nature’s Head toilet for ever but for a few years full-timing and then every once in a while after that it is just fine and worth the money. It’s well built.

  6. Great, Thanks for the info. We have also been fulltiming for 8 months, no problems with smell but all the screws on the sun-mar mobile came loose and fell out after driving down the I5. I am going to replace this unit with a Natureshead. By the way, I was originally using the sunmar peat moss mix, and have switched to free sawdust shavings from my power planer. (works great) Anyone with a planer has an endless supply of sawdust shavings. They easily stow away and are light.

  7. Send me an email and I will send you some pictures of my Motorhome. I built it myself with green building materials. Thx

  8. I was studying some of your content on the site and it’s great! Keep putting it up.

  9. So glad I found your blog. I will become a follower. Some useful ideas here.

  10. We use a NH and it has been great in our remote off grid cabin.

  11. Good stuff here. Will be bookmarking your page. Thanks for writing about your travels/life changes.

  12. Can a composting toilet be used in the back of a van? Do they all require electricity and if ventilation does not exist- could ventilation be easily added in a vehicle for units such as these?

    • Hey Diane – yes this unit could be bolted to the floor of a van. It does need a hose/ventilation outlet but that’s easy enough to add and it would also needs to run a 1 amp fan 24/7. That is also an easy enough thing to set up inside a van, since you will probably have golf cart or deep cycle batteries to run your lights, water pump, etc. An electrician could hook that up for you and the nature’s head comes with a flexible hose that could come up and out the roof of the van with a mushroom cap top. Any RV place could help with that too. I believe you could also set up an even easier non-electric toilet but I am not as familiar with those. Good luck.

  13. Thanks a lot for sharing. We have been searching for a composting toilet for our house and I think we are going to go with a SunMar.I’ll let you know how it goes after we use it for a while.

    • Brady – you are welcome. Good luck with the composting toilet – we love them!

  14. Way to go! I just wrote a composting toilet post today, so this is great.

  15. OK, I get it all, except for keeping the bowl clean. No water means streaking……. how does one solve that?

    • Hi Oscar – Good question. There is a sliding latch door that you open when you go #2. Once open the hole into the solids bin is big enough to just sit on the toilet, do your business and have everything go into the bin. No streaks. Once you are done you close it back.

  16. This was a great post. Many people cringe a bit over the “immodesty” of using an unconventional means of “disposal”. But do they realize that when the modern toilet first came out, many rejected it because it wasn’t as normal as an outhouse!

  17. Good information. We are thinking about installing a composting toilet and this helps!

  18. I’m in the process of selling my townhouse and buying a tiny house, and I’m looking into composting toilets. One question I can’t seem to figure out though – what do you do with the solids when you are on the move? Do you have a composter that sits in the back of a truck, or some other solution?

    • Hi Chris – Once full, we put all the solids in another container to sit for several weeks and then we empty the composted remains either in the woods or in a friends yard/garden, etc. depending on where we are. We always let the solids sit and finish composting before dumping though.

  19. Great post! I’m strongly considering getting a trailer in the near future and definitely want to go the composting toilet route. Where to you dump the liquids when on the move? Also, James, I’d love to see photos of your green RV as well!

  20. Cool project. I hope you guys are still enjoying it. We love our Nature’s Head so far and can’t imagine going back to anything else.


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