How Does a Composting Toilet Work?

So tell me, Deb, how does a composting toilet work?  Those considering going off-grid or buying a tiny home have asked me this question quite often.  I simply explain that it’s an environmentally-friendly alternative to the traditional flush toilet that turns human waste into organic fertilizer.  When they ask this question I can tell that they have some reservations and I don’t blame them.  I was a little tentative about composting toilets when I first heard about them too.  Most humans, including myself, have an aversion to poo and just want it to go away forever once it has left our bodies.  Living in the 21st century and using traditional toilets has allowed us to keep a distance from it by flushing it away unless something unfortunate happens like a clog.

How Does a Composting Toilet Work?

Composting Toilet: Pros and Cons


  • Composting toilets are environmentally-friendly.  They don’t waste water.  In the U.S., people using traditional toilets flush almost 7700 gallons of water each year.  It also makes use of human waste, a potentially nutrient-rich fertilizer.
  • It won’t pollute the ground water like a septic system potentially can.
  • You won’t have any water bills associated with your toilet.
  • Surprisingly, it doesn’t stink.  When someone does a number 2 (like my technical lingo?) in a traditional toilet, it can stink up a bathroom, but not a composting toilet.  Because a composting toilet has a fan that creates a steady vacuum that pulls the air to the outside, the smell is pretty much nonexistent.  Even the most basic bucket composting toilet doesn’t stink as long as you cover up your waste after you’re done.


  • Most of your house guests won’t understand it and won’t want to use it.
  • Due to the compartments, they tend to be a larger than traditional flush toilets especially the all in one units.

Types of composting toilets.

An all-in-one composting toilet

how does a composting toilet work - all in one
via Amazon

All-in-one composting toilets (AKA self-contained composting toilets) need less plumbing.  They have a smaller capacity so they need to be emptied more often. They’re also ideal for tiny homes on wheels.

A composting toilet with a separate tank (electric and non-electric)

how do composting toilets work - separate tank
via Amazon

Central composting toilets have a separate tank that will most often be in another room or another floor. This special setup needs additional pluming.  One of the benefits of this type of unit is that it can go long periods of time between emptying.  Another benefit is the toilet itself is similar in size to a traditional flush toilet.

Related:  Which Off Grid Refrigerator is Best for your Off Grid Home?

How Does a Composting Toilet Work?  The details.

A composting toilet uses evaporation and decomposition to transform human waste into compost. Because human excretion is 90% water, the fan and vent system are used to evaporate the liquid. What’s left is a small percentage of what went in and it can be used as organic fertilizer.

Most of the modern composting toilets have a urine diverter which just means that the urine goes into a separate part of the tank.  This along with the vent system really help to minimize odors.

After setting up and before using for the first time, empty the bacteria packet into the toilet.  This facilitates the composting process.

Any type toilet paper is fine.  It’ll decompose with everything else.

After you’ve done your business, cover all the solid waste and used toilet paper with something like peat mix/moss or saw dust.  This helps the composting process and gives the compost body.  It also helps with minimizing odor.

There’s a crank on the tank that needs to be turned about a couple of times a week.  It’s part of the maintenance and further helps with the composting process.

Once the tank is two thirds full or so, you can empty the contents into the “finishing drawer” by turning the crank the opposite direction.  This finishing drawer has a heating element and a fan to keep the composting active.  The compost needs to be kept in the finishing drawer for 6-8 weeks depending on the model.

That’s pretty much it.  Once your compost is finished, it’s broken down into a material that looks nothing like what you’d expect.  Some say it looks like potting soil and others have said it looks a little like sawdust material.

You’ve now got nutrient-rich organic fertilizer that you can use on your flower beds and non-fruit producing trees.  Now whether to use it on vegetables and fruit-bearing trees is hotly debated and I would advise you to do the research and do what’s comfortable for you..

This post should answer the question: how does a composting toilet work. If you’ve got additional questions, please feel free to post them in the comments section below.

Want to read more?  Check out other related content from our site:

5 Off-Grid Internet Options with Pros and Cons

Off-grid Living Inspiration: Jill Redwood

27 Ways to Make a Living Off the Grid


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1 Comment

  1. This is all news to me, I had no clue how a composting toilet works and yes, I thought the smell must be horrific but you just proved me wrong. It’s obviously a lot of work but when you’re serious about going off-grid I guess this is one of the first steps, especially when you think just how much water you can save this way.

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