How Does a Composting Toilet Work

How Does a Composting Toilet Work?

When people think of toilets, typically they’re imagining a standard flush design, using water to empty the waste into a septic or sewer system. There are places and times, however, where we may not have access to such amenities: living off the grid (in a cabin, for example), traveling across the country in an RV, boating for long periods of time.

Others may simply be looking for an eco-friendly way to dispose of their waste. Whatever the case may be, a composting toilet is a smart alternative. But how does a composting toilet work?

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What’s the Purpose of a Composting Toilet?

In order to understand the function of a composting toilet, it’s worth understanding what composting actually is. Put simply, composting is the process by which biodegradable material is decomposed by microscopic organisms under specific conditions. In the case of a composting toilet, you can easily guess what that material might be.

Once composted, if everything is done correctly, you can then safely use the recycled waste as a fertilizer of sorts. The process can save water, benefits those with gardens, and – through those two things – can end up saving you a lot of money. What’s more, in bypassing sewers and septic systems, composting toilets are a boon to the environment.

Now, back to the original question: how does a composting toilet system work?

The Three Keys of a Composting Toilet

A properly functioning composting toilet has three central tasks it must perform.

  1. It must evaporate the moisture or liquid within. A large percentage of the waste going in is liquid as is, and it should evaporate fairly quickly. Some composting toilets even have waterless urinals or at least separate compartments which can be removed and emptied. Regardless, a vent should handle most of the evaporation, sometimes with the aid of a heating system to speed up the process. As long as the compost isn’t completely dry (as the microorganisms need moisture to do their thing), you’re on the right track.
  2. Ensure that the composting process is fast and odorless. Like anything biodegradable, waste would break down given time, but the speed a composting toilet provides removes potential odors that would otherwise result. This speed is often achieved through bulking material, such as coffee grounds or sawdust, which brings oxygen to the composting microorganisms.
  3. Create compost that is easy and safe to handle. Naturally, plunging your hands into the toilet isn’t on anyone’s bucket list. With composting toilets, however, you’ll basically be handling soil. No, not “basically” – you will be handling soil. The look, smell, and feel of it should be proof enough. If that’s still too much, consider the fact that the best composting toilets on the market only need to deal with one or two times a year.

Composting Toilet Design

Of course, there are a number of variations on the basic composting toilet design. Some use bio-drums some channel liquid waste into separate containers; some have multiple chambers that serve various functions. What all composting toilets have in common is that they achieve the above three tasks in some way, shape, or form.

With simpler composting toilets, the waste goes directly from the toilet into a composting chamber. Given the right amount of oxygen, moisture, temperature, and bulking material, the microorganisms can do their best work. A ventilation system can be essential in maintaining these conditions, and many composting toilets come with one installed. Turning over the compost once in a blue moon can also help, and is in its own way a type of ventilation, letting oxygen reach previously buried compost.

Should your composting toilet have multiple chambers, a few more possibilities are added into the mix. Commonly found in the evaporation chamber, connected to the composting chamber by a screen. Excess moisture flows through the screen, then evaporates accordingly. Single-chamber designs may require the compost to dry outside of the toilet entirely, making the evaporation chamber quite useful.

Another common chamber is called a finishing drawer. As you might imagine, contaminating mostly composted material with new waste isn’t optimal. A finishing drawer avoids that by keeping older (but still unfinished) compost separate from the main composting chamber. It’s just a more organized way of doing things.

Types of Composting Toilets

Outside of the numerous design possibilities, it’s also important to consider the overarching types of composting toilets you can choose from. For those wondering, “How does a composting RV toilet work?” or, “How does a composting toilet work in a tiny house?” the distinction is essential. Luckily, there are only two types to deliberate between.

  1. Self-contained composting toilet. As the name would imply, this type is an all-in-one deal. That means where you find the toilet, you also find the composting chamber and any other features the design boasts. Not traditional-looking, but great for smaller spaces (like RVs and tiny houses!).
  2. Central composting toilet. With this type, the toilet is often more standard-looking. The composting chamber exists in a separate place entirely – often a floor below or somewhere outside – connected by a pipe.

Composting Toilet Pros and Cons


  • Smell No More: Handled properly, the smell is reduced greatly. It won’t completely leave, but less is more.
  • Long-Lasting: Most composting toilets work for a long time. That’s more money in your pocket.
  • Gardener’s Gift: You won’t need to pay for gardening compost. Great, right?
  • Pathogen Purge: Less need to worry about dangerous bacteria and pathogens.


  • Knowledge Needed: You can’t just flush and leave. If you don’t know your stuff, things can go awry.
  • Good Compost? The resulting compost may need to be treated before it’s ready to use.
  • More Parts: Certain models require extra parts to work.
  • Be Consistent: Without a fairly consistent source of waste and bulking material, the compost won’t form as well.


The question of “how does a composting toilet work?” is not a simple one, but one well worth answering. At once wallet- and environmentally-friendly, it’s a system with plenty of benefits all around. For those looking for a substitute for flush toilets, a composting toilet might just be the way to go.