How to Make a Vermicomposting Flush Toilet

Wendy Howard
Friday, 20th June 2014

How to create a composting toilet system with a flush toilet, a worm-composting bin and a filter bed. Nothing is wasted and the garden is given nutrient dense organic matter.

Quinta do Vale is an off-grid permaculture project of 2.5ha in the mountains of Central Portugal. It’s an evolving demonstration site for many aspects of sustainable living, with a particular emphasis on off-grid infrastructure. It’s run by Wendy Howard.

When I first started planning the infrastructure here, I intended to use Joe Jenkins‘ dry ‘humanure’ composting toilet system throughout. It’s simple, easy to construct and maintain, portable even, and doesn’t require separation of urine from faeces. And it’s an efficient thermophilic composting process with a well-balanced output. It’s no wonder Jenkins’ toilets have been dubbed ‘Loveable Loos’. What’s not to like?

Many people though dislike dry toilets. If there’s to be a mass movement towards better ways to deal withour sewerage, then this can’t be ignored.

In 2013, we were converting an old hen coop into an outhouse toilet. Coincidently, at the same time I came across Anna Edey’s experiments with vermicomposting flush toilets in Massachusetts two decades ago. It’s described on the website promoting her book. Edey's website didn't give full details, but there was enough information for me to work the rest out for myself. As it happened, the situation of the outhouse was ideal for installing a similar system, so that’s what I did.

From a conventional flush toilet, flushings drain through a waste pipe into an insulated plastic container. The container holds a large quantity of worms who inhabit the surface layers of a mass of carbon-rich organic material (wood shavings, bracken, leaf litter, etc. topped with a starter layer of half-processed compost).

When the flushings enter the container, the solids remain on the surface to be processed by the worms and the liquids drain through the organic filter material and exit the container. They then pass through another waste pipe to a growing bed, also full of carbon-rich material, where they’re taken up by plants or processed by soil bacteria.

I used a second-hand 1,000-litre plastic IBC to form the basis of the system. We made an access hatch by cutting half of the tank’s top out. It slots back into place neatly, held by the screw-top lid to the central opening (through which the waste pipe empties into the tank) and an aluminium bar which clips onto the frame each side. Once the tank was sited, we connected 110mm plastic waste pipe to the outlet and dug it into a trench leading to the growing bed.

The tank is sited immediately below the toilet in a dry-stone schist enclosure. As the walls were built, insulation was added to keep the worms within their optimum temperature range of 13-27°C, winter and summer. Closest to the tank, we used sheets of polystyrene insulation, and filled the gap between the insulation and the stone wall with Leca (lightweight expanded clay aggregate). A relatively lightweight galvanised corrugated metal hinged roof makes access to the tank simple. More polystyrene insulation was fixed to the underside of the roof and the top of the tank.

The growing bed, about 1.5m³ in volume, contains ½m depth of wood shavings, leaves, etc. to act as an organic sponge and carbon reserve. The black water is piped into the bed and flows through a branched system of perforated 40mm waste pipes laid in the upper layers of organic material. This one bed should be sufficient to deal with the comparatively small volume of liquid likely to be generated by the toilet (greywater goes elsewhere). The bed is unlined - there’s no possibility of contamination of groundwater or neighbouring properties and if there’s any seepage through the filter after large amounts of rain, it will simply contribute fertility to the fruit trees on the terrace below.

Once the water supply was connected to allow for flushing, the system was ready to go. The original plan was to start things off with worm-rich horse manure, but a cold wet February was the wrong time to find worms in the manure heaps. Instead I obtained a kilo of worms - about 5,000 Eisenia fetida or tigerworms - from ebay and added them to the tank along with some recent additions to the humanure compost heap and some kitchen scraps. We then started using the toilet. The green filter bed was backfilled with topsoil and planted with a lemon tree. More nitrogen-loving plants will follow.

During the initial settling-in period, there was a slight smell from the container, but it disappeared within a week and the system is now working well.

Quinta do Vale is fundraising to complete its communal building, the hub of the quinta's activities for interns and volunteers, and an educational facility for workshops and courses. It employs people from the local offgrid community to do this, so all money raised is supporting their projects too. Check out their crowdfunder here: 

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Further resources

How to make a DIY worm tower


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carolinepetherick |
Fri, 20/06/2014 - 18:20

What happens when the IBC if full of worms and processed poo?

Wendy |
Fri, 20/06/2014 - 21:51

Good question, Caroline. Anna Edey writes "The truly astonishing fact is that the more I put into the box, the less there is in the box. As I write this, in October 1997, 25 months have passed since the installation, with usage ranging from one to seven people. This box has by now received approximately 2,500 flushes, 140 rolls of toilet paper, and 35 cubic feet of leaves and woodchips (the original 12 cubic feet plus periodic additions). The action of the earthworms and other bioorganisms has reduced it all to about 9 cubic feet of magnificent earthworm castings. Even with all my previous experience I never would have expected this could be possible."

So I am anticipating much the same sort of thing with this system. If it ever does start to get to the stage of needing emptied, then we'll stop using it for a few days, entice all the worms up one end of the tank with some fresh food, and remove the composted material for adding to our growing beds. Then add some more woodshavings, etc, and start using it again.

Liz Spencer |
Sat, 28/06/2014 - 17:27

How do you keep the tank from becoming anaerobic?

Tristan Fransen |
Sun, 29/06/2014 - 08:07


First; Great idea, good thinking!
I was wondering about de filterbed. You discribe planting a lemon tree and other plants on top of it? Have you had any plantroots blocking the drainage-pipes underneath de filterbed? I can imagine they really like the nitrogen-rich pipes full of water.

Good luck with you project,


Wendy |
Tue, 29/07/2014 - 11:19

Liz the tank has no incentive to become anaerobic. The flushings drain straight through the wood shavings/leaves/bracken layer and exit the tank fairly soon after flushing. Because of its structure and composition, this layer also traps a lot of air within it. The worms ensure the compost layer is aerated. Periodic additions of more woody organic material will be necessary, but I anticipate no problems with the system going anaerobic. About the only thing that might make that happen is if the outflow got blocked and flushings were trapped in the tank. We would know by the smell very quickly though if that happened - probably in enough time to save the worms.

Wendy |
Tue, 29/07/2014 - 11:29

Tristan I wrapped the perforated pipes in fairly substantial horticultural fleece to discourage roots finding their way in. Clearly that won't last forever, but its unlikely the lemon tree would manage to block all the holes and pipes of the matrix, particularly since flushings are periodic rather than there being a constant trickle of water attracting the roots. I will probably use annuals like tobacco for the remaining plantings, so other root systems will not persist and become a problem.

Pennyfeather |
Mon, 29/12/2014 - 18:15

I truly love this idea and plan on implementing a similar system. As I begin compiling information and resources, I do have a fundemental question. Cleaning?

Since it is a flush toilet, how do you clean the toilet so that you don't damage the worms or the composting environment? Is there a switch that allows you to divert the cleaning black water elsewhere? I am presuming that organic based cleaners are used, but is there one (or more) in particular that is best for this type of system?

Thank you for the great article.

Julie Longpré |
Sat, 24/01/2015 - 02:57

Hello and thank you for this article.
Would this compost be safe for human consumption? What preparation would the compost require if any?

D.Aragon |
Mon, 26/01/2015 - 14:23

A principle problem with conventional on site waste water systems is that the solids have to be pumped, hauled, and then treated in a conventional waste water treatment facility. This is a great solution to that for us resource aware rural-ites.

However, caution is appropriate here. Those conventional systems with their subsurface drain fields are engineered according to system and site specifics that include # of users, depth to groundwater, and soil types and conditions. Even in these engineered systems, problems often arise with the drainfield (where the waste water is eventually dispersed underground for biological treatment). In the field of hydrogeology, biological contamination from on-site waste water systems is a classic source of aquifer contamination.

So, there is always a possibility of groundwater contamination. And, it would be good to consult a professional or do lots of self directed study in designing parts of the system that come after the worm bin. Especially as rural properties that would be most likely to adopt this type of system likely have shallow drinking water wells that are especially vulnerable to this type of biological contaminant.

Keep going!

Wendy |
Wed, 04/02/2015 - 07:55

Pennyfeather, in answer to your question ...

I use water and a good brush for cleaning. Nothing else is necessary.

However, were you to want to use bleach or conventional toilet cleaners, the system would be capable of handling it. According to Anna Edey, who originated it, she deliberately used all manner of cleaning materials to see how the system would respond to them. The worms were fine.

Wendy |
Wed, 04/02/2015 - 08:04

Julie Longpré, in answer to your question ...

I wouldn't recommend eating compost. But I presume you mean using it for growing vegetables and other edibles? Anna Edey doesn't recommend it, despite tests showing the resulting compost has no trace of pathogens or anything else remotely harmful. I understand her caution given people's extreme attitudes about faecal material. She was trying to get a system permitted for widespread use.

I have no such qualms as I already use compost from my humanure heaps in growing beds. No ill effect whatsoever and neither would I expect there to be.

Wendy |
Wed, 04/02/2015 - 08:24

D.Aragon, in response to your comment ...

Just because this is an amateur installation doesn't mean it wasn't engineered to take into account # of users, depth to groundwater, and soil types and conditions!

As for groundwater contamination, these slow-release carbon filter systems consisting of wood shavings, dead leaves, dried bracken, etc, plus worms and a bit of compost have been used to treat septic tank outflow. The originator of the system, Anna Edey, installed such a system for a harbourside restaurant handling around 4,000 gallons per day. For this system, "lab tests showed a 90 percent reduction of the total Kjeldahl nitrogen, from 86 ppm to 8.1 ppm, and a 96 percent reduction of the ammonia-nitrogen, from 77 ppm down to 2.5 ppm ... the flow-through took less than 10 minutes, and the foul odor was totally removed."

I'm in the process of drawing up a proposal, together with a local architect, for using such a system to treat a village septic tank outflow here which is currently discharging illegally directly onto the land and down into a river. This is mountainside land with soils averaging only 20-40cm deep, a slope of between 30-45° and no level ground for a leach field. Or even reed beds. No simple solution from the conventional armoury would appear to exist.

If we succeed in persuading the environment agency and local authorities to try a proof of concept with a succession of these biofilters, then we will have the experimental results to take this further. It offers enormous potential. I highly recommend you to read Anna Edey's website on the subject which is now back online having been down for the last month or more.

Krystana Shuley |
Sun, 15/03/2015 - 10:23


great article - I'm very inspired and getting ready to install a similar system. However I do have one question being - the tank that contains the worms- how thick does the layer of organic matter (wood- shaving etc) have to be when the tank is started.

Wendy |
Fri, 10/04/2015 - 10:25

Krystana - in answer to your question ...

I started the tank 2/3rds full of organic matter. So that's 0.7m³ of material. It doesn't have to be exact. If you used less, you would need to top it up sooner is all, but I wouldn't fill the container less than half full. Within a year, the worms had reduced this 0.7m³ of material to about 0.1m³. I was a bit concerned when I discovered how quickly they'd processed it as we had a cold winter and I was worried the worms wouldn't have enough material to stay warm, but they were fine. So I topped it right back up to the 2/3rds mark and will check it sooner this year to make sure they have more material going into winter.

Jeff Bosch |
Sun, 06/09/2015 - 19:39

Have you considered using black soldier fly larvae in addition or instead of the worms?

Catryna White |
Sun, 06/09/2015 - 20:08

We are a 7 person family. I was wondering what size would be needed for that many people? Thank you. Or would it be better to have 2?

Wendy |
Fri, 25/09/2015 - 22:30

Hi Jeff. The worms work so well in this system that there seems little point in messing with it on the principle that if it ain't broke ... But I'm very interested in bringing in BSF larvae (for poultry feed) and intend to devise another system using them at some point.

Wendy |
Fri, 25/09/2015 - 23:58

Hi Catryna. There isn't a lot of data available on the use of vermicomposting as primary sewage treatment yet, so anything I say is basically informed guesswork based on what I know of Anna Edey's system (which has now been in use for over 20 years and has never needed emptying!), my experience, and the reading I've done on the subject. With that proviso, then it's possible you would be able to use a tank of just 1000 litres, though that does depend on whether you're planning on putting your grey water as well as your black water through the system. My experience is with black water only, and after over a year in use, my system will effortlessly handle fluctuating numbers of people using it - anywhere between 1 and 10 people - with regular periods of 4-5 people over several weeks at a time in a way that gives me a sense there is quite a bit of spare capacity in the system.

It's the volume of worm compost, organic material and live worms that's critical to the effectiveness of the system. As a living system, it's self-regulating and will constantly adjust itself to the amount of 'food' available, but with 7 people, you would need to start the system with more worms than I did. It will take the worms a few months to build up their population to optimum levels and it's likely you would need to add organic material more frequently then I do (which is every 6 months).

If I were building a system for your household, then I would build it in such a way that I could easily add another tank on if it were needed. It may never be needed, but it's good to have that flexibility ...

HealthNut2 |
Thu, 24/03/2016 - 12:58

To Pennyfeathers question about harmful chemicals used in cleaning the toilet..... I would highly recommend anyone using this method to check out Basic H2 by Shaklee. If anyone would like to know how to get it directly from the company at a discount they can contact me at Better Earth-Better Heath on Face Book.
I would encourage all your readers to consider using Shaklee Get Clean products as they are non-toxic and the fastest bio-degrading cleaners in the world. Jeff I would love to speak with you personally about these products. They will change the direction of contamination that our fragile planet is headed in.
Most sincerely,

Wendy |
Wed, 09/11/2016 - 21:54

Hi Maria. Yes. All IBC tanks have a tap outlet at the base of the tank. You connect this into your pipework leading to your 'greenfilter'.

MariaMF |
Thu, 18/08/2016 - 19:46


Is the outlet pipe from the vernicompost tank into the mulch bed right at the bottom of the tank?


PermacultureIT |
Tue, 14/03/2017 - 10:35

Hi there, I am seriously impressed by this system. It requires no 'reprogramming' on the part of the user except that only biological cleaning products should be used and nothing except what comes out of your body can go into the toilet. This is just simple common sense.

Would it be possible to do an update on this system? It seems too good to be true :) Exactly what I've been looking for.

NannyWise |
Tue, 25/04/2017 - 01:28

Hi there, I love vermiculture and had much success making a vermiculture composting system.. I'm very interested to experiment more with it.. However, my concern with your system is really the 'green filtration/ growing bed' after The tank. Surely if you are flushing water and pee through the tank of poo and organic materials, the water will be contaminated with coliforms and pathogens, and releasing this to drain away under the earth and to the terrace below, is potentially damaging to groundwater and fresh water eco systems. How can you guarantee that your system is safe? Thanks.

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