The Clivus Multrum Composting Toilet and Greywater System

June 17th, 2020

Dear Readers, 

The Clivus Multrum composting toilet is kinda cool in that its name gives the bases of how it works in two words. ‘Clivus’ is Latin for ‘incline,’ and ‘multrum’ is Swedish for ‘compost room.’ And, in essence, the Clivus Multrum composting toilet is a toilet (basically a hole) that lets waste fall into an inclined composting room. Bam. Boom. Blog is basically done. 

Ha! Kidding. To give justice to the simplistic yet holistically functional toilet system, it deserves a slightly more in-depth explanation. I promise, this will be simpler than the blog about wastewater treatment facilities…

Their toilets are much more sophisticated looking than a dark, deep hole you squat or stand over. They actually look like a real toilet! Some even use a small amount of foamy, soapy water (no more than 6 ounces) to clean the bowl when you use the flush mechanism…it’s like you would never know that you just sat on top of, and contributed to, compost.1 

When you donate your waste as tribute to earth fertilizer, it falls down into that inclined chamber. This incline is super important: it is what keeps the urine and the poop from being one, large, smelly, conglomeration. Gravity forces the urine to filtrate downward through the solid wastes, allowing the solid waste to remain dry (and unsmelly). However, when the urine gets to the bottom of the chamber…it is no longer urine…like a butterfly, the caterpillar has gone through metamorphosis!  

“How the Clivus Multrum System Works,” Credit: Clivus Multrum, Science & Technology 

Wanna know the secret to changing your urine to something else (maybe not necessarily as pretty as a butterfly…)? I sure did…

Remember those crazy oxygen-hyped up, ravenous microorganisms which broke down organic matter in wastewater treatment plants?2 Well, the Clivus Multrum composting toilet has recruited the forces of those same microorganisms…and they devour the nasty stuff in your solid and liquid waste like starved zombies. As the pee filtrates downward through the solids, the microorganisms’ feast causes the “chemically unstable components of urine- urea and ammonia,” to turn into a liquid containing “nitrite and nitrate.”3 This liquid, depending upon local regulations, is a suitable fertilizer once it is automatically pumped from the compost chamber to a seperate tank. 

The solid waste left in the chamber is joined by “bacteria, fungi, insects and compost worms”….which you manually put in before usage.4 While it seems barbaric to inflict such torture upon living organisms…they love it! It becomes an even bigger feast, and they break down the poop into a compost. The devouring (there is so much eating in waste management…) causes the accumulation of solid waste to decrease in volume by 90%. Ninety percent!! This allows the tank to only have to be emptied of its solid contents (at the most!) once per year. They even recommend waiting several years before removing the composted waste. As with the liquid fertilizer, the solid compost may be used where local codes allow. 

The whole composting system…the breakdown of urine and feces…does release CO2 and water vapor. A vent with an ongoing fan keeps the CO2 and water vapor out of the tank, and keeps the system, as well as the bathroom, odor free. William and I are curious how this vent will work with a Passive House…

The greywater system is also fairly simple. ‘Greywater’ is the water that comes from sinks (except those with garbage disposal units), dishwashers, clothes washers, bathtubs, and showers. Greywater is NOT to be confused with blackwater, which is the water that comes from the toilet. Because greywater has not been exposed to our human waste, and therefore decomposes much quicker (resulting in a disturbing odor), it is released directly outside into an 8 to 12 inch layer of soil. This soil provides an aerobic environment (plentiful in oxygen) for all of those hungry microorganisms which stabilize the greywater. Plants are grown in this soil and absorb much of the greywater nutrients. This group of strategically planted plants are rightly called a ‘greywater garden.’ 

A few considerations William and I need to take into account with the incorporation of a composting toilet and greywater system: 

  • In regards to our ‘pipe-dream,’ William and I are curious as to how we shall achieve the efficient placement of prefabricated homes when we will also have to plant a greywater garden for each home. A greywater garden is certainly something we are excited to try out with our own home, The Seed. 
  • The composting tank’s size, and the accessability of maintaining it, need to be accounted for in our home’s design plans. As of now, they are not.
  • Depending upon the exact township in which we build our home, what are their regulations regarding the usage of human waste fertilizer?
  • Again, depending on the township, what are their regulations regarding the Clivus Multrum greywater system? 

As an idea, the Clivus Multrum composting toilet and greywater system is ingenious. In practice, in both rural and urban areas, Clivus Multrum has proved their idea to be successful. As two young idealists who wish to raise a family in this home, we see this as a perfect opportunity to test out seemingly idealistic ideas. 

Thanks for reading!


Shelby Aldrich

1. “Products and Services,” Clivus Multrum, Inc. 2010. Accessed on 10 April, 2020.

2. Do see “Our Waste Goes Where?” for further reference…

3. “How the Clivus Multrum System Works,” Clivus Multrum, Inc. 2010. Accessed on 10 April, 2020.

4. “How the Clivus Multrum System Works”


  1. Decisions, Decisions, Decisioons!

    Love you, Aunt Rose

  2. Wait—where do these systems go in relation to your water pillow?

    • Hey Aunt Deanna! These systems are actually not connected to our water pillow. Think of it as ‘input’ vs. ‘output.’ The rainwater pillow is our ‘input,’ and provides us with our drinking water, water to shower, wash our hands, do laundry, dishes…and then that water, the ‘greywater,’ will be released to our greywater garden (the ‘output’). We do still need to figure out how exactly we are going to fit our rainwater pillow with our composting tank and liquid fertilizer tank in our home’s designs. They all should be contained in the home’s building envelope so that they can be thermally conditioned. William and I are still pondering that part! 🙂

      • Oh, I got that they are separate, but you have a lot going “under” your little house. Was there a schematic that shows greywater, black water, and water pillow? I am just curious as to how it will all work logistically.

  3. Thanks for the write-up on the Clivus Multrum system! After 3 years I’m curious how it’s working? Pros & cons and anything else would be great to learn about. We’re thinking about the CM or similar with the M300 tank appearing to be what we would need in our home.

    Best wishes

    • Hello, Chuck!

      Thank you for reading! 🙂

      Unfortunately, William and I have decided to not go with a composting toilet due to a mix of DEP regulations and feasibility within our local area. The PA DEP allows composting toilets, but disallows the use of the liquid and solid fertilizers on private land. We would have to have the fertilizers pumped and taken elsewhere. We did eventually find a local septic management business that is registered with the DEP to take septic tank waste (and compost toilet waste) and treat it to be used on their farm fields! Which is super neat, and allows the waste to be used as fertilizer in the end. However, the Clivus Multrum system and their pumping capabilities were not very compatible.

      Soooo…we are now going with a traditional sand mound system. Which! We can still have the septic tank pumped by the same local septic management business and have it used eventually as fertilizer. Only downsides are the increase in water usage (but, we did find some nifty .8 gpf toilets…) and the disruption of root systems and native soils for the sand mound (but…we do have a friend with an ecology background who is helping us to turn the septic system into something ecologically beneficial to our site and the surrounding habitats). Trying to find the positives amidst disappointments!! 🙂

  4. Shelby thank you very much for your kind, informative reply! In another family home we use a gravity drainage (digestive) system which finishes in a reed area and it works very nicely … so perhaps close to what you will eventually have in play. Best of luck with that – you don’t need the luck 🙂 – and congratulations on taking a responsible approach to environmentally sound solutions. We all need to follow your wonderful example! Yea!
    We have built a hempcrete home at approximately 1200 meters on the western slope of the Mont Blanc Massive, Haute Savoie France, and are very pleased with it. If you wish to take a tour sadly we are well behind in our posting (this is the year we bring it all up to date! heh heh fingers crossed) but on either Instagram or Facebook (believe my wife still has an account) you can search for asinglething and find some info re our aims and methods.
    We will use a dry composting system and I will probably design a tank to have manufactured using stainless steel simply because of my concerns about use of plastics (we have of course used some as well) and the release of bisphenols into the water systems.
    Onward! And again very best to y’all in your wonderful home 🙂
    Please don’t hesitate to contact me directly via email if you wish.


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© 2020 Sustaining Tree