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Experiences with grey-water and composting toilets?

user-757117 | Posted in Green Products and Materials on

Grey-water toilets: The Aqus toilet system ( like the most popular (only?) grey-water toilet available. I really don’t like the fact that it installs with a purification system and electric pump. Does anyone know of a model that does not have these features?
The concept is simple enough. Has anyone tried making their own grey-water toilet? I’d like to consider using sink drain water to fill the toilet tank and also possibly a small reservoir so as to have two flushes available on demand. Surplus drain water would overflow into the toilet drain.

Composting toilets: Looking for generalized experiences with any type of composting toilet. I have looked at a non-electric Sun-Mar brand toilet close up but didn’t like the 4″ PVC vent pipe that must be installed (with no bends) through the roof to a height 2-3′ over its peak. Is this a typical requirement?

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  1. Riversong | | #1


    You'd better check your local codes. In some jurisdictions, greywater cannot be used for toilets without filtering and disinfection, since microorganisms can grow in the toilet tank. Additionally, some jurisdictions (like here in Vermont) consider kitchen sink and laundry water as septic and cannot be diverted to greywater systems. The best use of greywater is in plant bed irrigation, since the soil organisms and the symbiotic root organisms will bioremediate the organics in the water and feed the plants. Indoor planting beds can be used as well as outdoor constructed wetlands.

    All composting toilets require a passive vent, at a minimum, and typically a low-volume fan to evacuate smells and flies and to evaporate excess liquids (which is most of the volume of human output). Some also use a resistance heater to evaporate liquids and encourage composting. All the self-contained composting toilets are too small for effective composting. The only true composting units are the large-volume ones with isolated compost chambers, like the Clivus Multrum and Pheonix (which may be the best of the lot), but the compost chambers must be in a heated space for them to function.

    With the small self-contained units, you have to be careful not to overpower the vent fans with a bathroom exhaust fan, which can backdraft the smells from the toilet. There are some urine-separating "waterless toilets", which are not composting toilets but just fancy bucket latrines that require separate composting of the solids. You can build your own bucket latrine for very little money if you want to compost your humanure outdoors.

    A plumbing vent does not need to be above the ridge, just high enough to avoid burial in snow. However, without a shanty cap, downdrafts from winds coming over the ridge can reverse the air flow. Exiting near the ridge is always a good idea - for maximum height and draft, to avoid downdrafts, and to prevent sliding ice and snow from shearing off the pipe.

  2. Riversong | | #2

    By the way, I designed and built the first state-approved composting toilet in Massachusetts 12 years ago. It was built into a corner of a super-insulated modified Larsen Truss home, with two CMU composting chambers each sized a year of output for a family of four. This allowed each side to be filled for a year and composted for another year before being emptied. The compost chambers were insulated on the outside with 4" of XPS and had outdoor, insulated and gasketted cleanouts. They were also built on a radiant slab.

    There were two "thrones" in the toilet room above, with an adjoining but separate bathroom (doesn't it make sense to separate the waste and washing functions?). Each thrown had a couple of fresh air inlets, which directed conditioned air down to the lower liquid chamber (solids held up on plastic mesh on plastic milk crates), across the liquid for evaporation, and up to a 6" vent that went through the roof, capped by a turbine to increase updraft when the wind blows, and with an inline Fantech fan on a variable-speed switch.

    I had hoped that the heat of decomposition would be enough to maintain a passive draft, but the units required the fans on very low speed to keep flies under control, prevent escaping odors and - most importantly - to evaporate the high volume of urine (80 gal/person/year). We did not want to divert the urine since adequate moisture is critical to composting, and the toilet was "flushed" with coarse carbonaceous material such as wood shavings (and kitchen scraps) to help maintain an aerobic environment and to establish the critical 30:1 C:N ratio.

    This toilet, which was modified from the "moldering toilet) developed by the Farralones Institute of CA and the Permaculture Center of NH, functions as a true composting toilet and is a vast improvement on any of the manufactured units on the market.

  3. GBA Editor
    Martin Holladay | | #3

    In the 1970s, I built two composting outhouses, which require no electricity. I followed Sim Van der Ryn's plans; you can read more in a book called The Toilet Papers, or read about the design online:

  4. Daniel Ernst | | #4


    My experience with indoor composting toilets has been limited (a few weeks), but largely negative. Enough so that I went a different direction. As Robert pointed out, the self-contained units (toilet sized) are too small to allow complete breakdown of the organic matter. They are finicky systems; they require the perfect moisture balance. Too much moisture, the composting chamber gets overwhelmed with anaerobic bacteria (these organisms process the organic material more slowly and produce more noxious gases compared to aerobic bacteria). Too little moisture, the microbial action is reduced or delayed. The limited size of the organic mass makes them more sensitive.

    Passive ventilation systems are just that; they don't always work the way you would like. You can go with the active systems, but IMO, having an electric resistance heater or a 10W fan running on the vent stack detracts from the overall simplicity and design of a composting system.

    Do you have kids? If so, throw that into the mix as everyone in the household, as well as guests, will need to know how to operate the composting toilet.

    Robert and Martin mentioned site-built systems, as well as the larger manufactured units. There is another alternative that has a MUCH lower initial cost; it's extremely effective and easy to maintain. There are no odors. There's no vent stack or electricity required. Kids can easily learn how to "operate" the unit.

    Have you heard of the sawdust toilet?

    Joseph Jenkins in the pioneer on this topic. His "Humanure Handbook" is an excellent read. Even if you decide to go another route, the information on the composting process is very informative:

    For most people, the idea of shitting in a bucket is not groovy: it's backwards (apologies for the language, but let's not be bashful). I've taken all sorts of grief from extended family and friends for my use of a sawdust toilet. Fact is, most people are fecophobic - and full of contradictions. They will pick up their dog's waste each day, but can't stomach the sight of their own waste except for a few seconds as it's flushed down their shiny white porcelain bowl. I'll get off my soapbox on that topic now. Suffice it to say that whatever greywater or composting system you choose, expect resistance.

    At the start of my composting journey, my wife wasn't in agreement. So we tried the sawdust toilet in an outdoor setting as a trial. She liked it enough that she was happy to move it inside. Although we had a regular "flusher," our family used the sawdust toilet. It was a good transition.

    Benefits of the sawdust toilet:

    • Low Cost - Do you have an empty five-gallon container handy? Access to a local sawmill?
    • Easy - Cover your waste with sawdust. Two simple rules: no exposed waste, no visible wet spots. You don't have to worry about moisture balance or the carbon / nitrogen ratio.
    • No Odors - The composting takes place outside, under a thick layer of straw or other fibrous material. Indoors, the cover material (sawdust) keeps the odors from escaping.
    • Full Breakdown - You fill the composting bin one year, let it sit another. It goes through the full composting process: thermophilic bacteria start, fungal organisms and earthworms finish. It's as sanitary as you can get.
    • No Code Issues - Nothing in the code regulates outdoor composting ;) Not so with greywater systems . . .

    The drawback is you have to empty the buckets. For my family, four buckets once every 5-6 days. But think of all the wonderful compost you'll have available for your gardening.

    Although Robert has mentioned the "bucket latrine" a couple of times on this forum, I'm surprised not to see it promoted on the GBA website. There at least ought to be a link on their "Composting Toilet" page (hint, hint GBA). Or maybe they could make it the topic of a future blog. I guess what I'm saying: humanure ought to be a searchable word on this site.

    Good luck!

  5. Riversong | | #5


    Good segue into a more sensible approach to waste management. My current client is building on a small lake-front lot (actually re-building where her old family cabin used to be), with an unknown grandfathered septic system (and can't afford a new pumped system with pretreatment) and so wanted two composting toilets. After much research, she realized that most people who've used them have had bad experiences (and, I agree with you, that's largely due to our phobia of fecal matter and our habit of "out of sight - out of mind"). Unfortunately, she ended up purchasing two small "waterless toilets", which are nothing more than very expensive bucket latrines with a vent fan. For a small fraction of the price, she could have built very elegant "thrones" for indoor bucket latrines which would not require venting.

    But there are codes which may inhibit outdoor composting of humanure. I know that in MA, where I built my first indoor compost toilet, even the fully-decomposed compost is required to be buried under 6" of soil (or disposed of at a sewage-treatment plant), there can be no liquid effluent into the environment, and NOFA (the organic farm association) will not allow composted humanure on certified organic plants (except fruit and nut trees).

    But I use a bucket outhouse with a pail of mixed wood shavings and sawdust for "flushing", and have two compost piles next to the outhouse - one active and one inactive. In the winter, when the bucket freezes and fills up too fast with the cellulosic material, I "flush" with granulated limestone (from my local garden supply) and burn much of the paper in an antique cast-iron 3-legged kettle on the floor.

  6. Expert Member
    ARMANDO COBO | | #6

    I'm just LMAO (with tears and belly rolls) just thinking about my high-end clients and all of them having to use one of your proposed latrines and composed toilets.... Great reading guys!!! Just curious… what do you all use for TP??? This is just to funny.... ;-)))))

  7. Steve El | | #7

    I know I believe a composter should effect (a) resale value and (b) resale desirability, which are very different things. I think if the world worked sensibly both would increase considerably. Does anyone have real world experience with what actually happens?

  8. Lucas Durand | | #8

    Thanks for the all comments and links.

    At the start of my composting journey, my wife wasn't in agreement.

    We have this in common. It sounds as though an outdoor system might be best for many reasons and not just in getting my wife to come around to the idea.

    Robert and Daniel, do you protect your compost piles from the rain?

    For most people, the idea of shitting in a bucket is not groovy: it's backwards

    In Asia, the process of collecting and recycling human waste is ancient. Check out this interesting article on sustainability during Japan's Edo period:
    It contains a list of occupations filled by people at the time, including "Human waste dipper". There is also mention that humanure was, until about 1955, the most important source of fertilizer available to Japanese farmers. I find it hard to snicker at a system that for hundreds of years sustainably supported food production for population numbers unheard of in any other part of the world.

  9. Lucas Durand | | #9

    The best use of greywater is in plant bed irrigation, since the soil organisms and the symbiotic root organisms will bioremediate the organics in the water and feed the plants.

    Robert, let's set aside regulatory issues for the moment. In my cold climate (10000+HDD and decreasing) I am having a hard time adapting outdoor greywater drainage systems for winter use. I did see one plan where a greywater drain emptied into a bed that was deeply mulched with leaves for the winter. Once covered with snow the idea was that the bed, under its insulated blanket of leaves and snow would not freeze...
    What do you think? Have you ever seen anything like this?

  10. Lucas Durand | | #10

    It may well turn out that your high-end clients will at some point be forced into using a bucket latrine before the next decade is out. I doubt they'll be laughing though ;)

  11. Riversong | | #11

    It would be poetic justice if all those "high end clients" were forced to become the "human waste dippers" in the dystopian near future.

    Lucas, a 16-home upscale intentional community with several straw bale homes in Charlotte VT (7700 DD) uses a constructed wetlands for wastewater pretreatment for all the homes, so it clearly functions year round. I'm not sure what would be required in your climate, but perhaps an attached greenhouse/sunspace with container wetlands or hydroponic vegetables would be appropriate.

  12. Daniel Ernst | | #12

    It's okay Armando, it really is a funny topic. You should try reading Joe Jenkin's "Humanure Handbook." It's full of belly rolls and giggles. You can find out how to "turn turds into tomatoes." Only then will you understand the Tao of Compost (one of his chapter titles).

    Have you ever seen the movie "The Matchmaker" with Janeane Garofalo and David O'Hara? There is a scene in there where one of Senator McGlory's supposed Irish relatives finds his dentures in the shit bucket. What a great film and great scene ;-)

    You are quite right. High-end clients and sawdust toilets don't blend well. Reminds me of the fact that the French nobels once had servants that would wipe their royal asses. Talk about fecophobes! Ha!

    But down here on planet earth, humanure has a rich history. Flushing our waste into a sewer system is a fairly new practice. And processing it in water treatment plants is even more recent. In some cases major cities didn't start processing their "effluent" until the 1950s - take Richmond, VA for example. They dumped it raw into the nearby rivers.

    Composting our own waste keeps the nutrient cycle intact. There's no sense in flushing valuable nutrients into our rivers and creating larger and larger dead zones in our bays, estuaries, and gulfs.

    And how funny is it that we consider it normal to defecate into 1.6 gallons of highly-processed, sanitized, fluoridated, tested and certified drinking water?

    Lucas you are right about Asian countries commonly using humanure. Only problem is, some of the lesser developed countries use it in a raw form (before any composting takes place).

    Whether you protect your compost pile with rain really depends on your climate. Usually not. The sawdust and other organic matter is like a huge sponge. Water is needed regularly to maintain the composting process; most of it evaporates via the heat generated by the aerobic bacteria. And humic acid has a great water-holding capacity - that's one of its primary benefits in soil. If you are worried about leaching, then start your compost pile on a thick bed of straw or other coarse organic material.

    I don't think the mulched-bed greywater system is workable for your climate. I investigated using this system in a 4,000 HDD climate and decided against it due to freezing / absorption / capacity issues (plants don't need much water in the winter). Cold weather inhibits or stops microbial activity, so the greywater isn't processed well.


  13. Expert Member
    ARMANDO COBO | | #13

    Hey, I was making fun of good and interesting reading. I’m learning quite a bit about composting toilet design in Martin & Daniel’s links… It also reminds me of growing up in South America where my family had two farms up in the mountains w/o any electricity, so we use Coleman lamps and candles; no potable-running water except spring fed and “filtered” by a clay pot on one and Zinc roof collected water on the other and open waterfalls for showers. Also, it reminded me of when we went into jungles; we had to go “al fresco” for our needs… we learned pretty quickly what plant leaves were good TP and which were not. Been there, done that!
    I also know its easier to do those systems in rural or semi-rural areas versus 10 million outhouses in NYC, LA or any other metro area. Imagine the health risks and infrastructure nightmare. So, I really don’t think anytime in the future we are going to see latrines and compost toilets in high-end golf course subdivisions or in a high-rise building in NYC; and that is what is so funny to imagine….

  14. Daniel Ernst | | #14

    C'mon Armando, that rich compost would work well to fill the all of the divots in that golf course. ;-) I'm not so sure about the high-rise solution.

    Lucas - This link is probably most relative to Armando's climate, but there is some good information here on greywater:

    Jenkin's uses a pond / wetland area to filter and process his greywater. Of course, you would need the perfect setting for such a system.

  15. Steve El | | #15

    Re, Robert's mention that "perhaps an attached greenhouse/sunspace with container wetlands or hydroponic vegetables would be appropriate."

    Back in the late 70s/ early 80s, I was captivated by a story in some newspaper or magazone (most likely the MPLS Star Tribune) of a university experiment that put a household's raw sewage in one end of greenhouse hydroponic beds, and out the other end of the snaking trough they got water cleaner than what the city sewer plant considered "treated" and put back in the river. I keep hoping someone revisits that.

    For the posters job, I wonder if the raw amount of material would matter? There must be a complex balancing act between climate, soil type and behavior, microbial population and heat producing activity, and climate. Perhaps an entirely different approach is needed for a single home versus a whole group of them?

    Just questions, no answers.


  16. Lucas Durand | | #16

    Fair enough Armando. Re composting toilets in the city: The C.K. Choi building at the University of British Columbia uses only composting toilets because of (I believe) its close proximity to a wetland. If memory serves, those toilets serves the needs of 300 employees... I'm not sure what type of composting toilets were used.

  17. Lucas Durand | | #17

    Daniel, thanks again. I have surfed around the Oasis site but as mentioned reliable solutions seem to be hard to come by when the ground is frozen from november to april.

  18. MICHAEL CHANDLER | | #18

    Lucas Back when I was living at my great-great-great-great-grandfathers (1791) farm in Maine about 30 years ago we just ran the chamber pot out to the compost pile before it froze. A bit challenging to winter house guests, but so was the ice freezing in the glass next to the bed at night. May have been some yellow snow just west of the back porch...

  19. Lucas Durand | | #19

    May have been some yellow snow just west of the back porch...

    Good for whatever's growing there come spring melt ;)

    Based on some of the experiences here, I think I'll put my energy into building an outdoor composting toilet. We're planning an outdoor wood-fired sauna anyway so maybe the two can be incorporated.
    I'll have to figure out some type of grey-water recycling system for the interior flush toilet that cuts out the electrical/chemical components. Water supply for the house will be well/rainwater cistern and I can't bear to see my precious clean water wasted on moving poop down the sewer line.

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