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How To Build A Composting Toilet

Composting Toilet

Have you ever considered, “What if our modern plumbing system were to fail?”

Things could get really, really bad quickly, if you have never had to deal with human waste.

A composting toilet or sawdust toilet as people used to call them, could be a simple answer. There are some important things you should know before you jump in head first. Let’s begin with how and why a composting toilet would be a great alternative.

Just What is a sawdust toilet?

Simply put, a composting toilet turns excrement into a small bio-digester and converts waste into inert and safe compost. The idea is the same as composting leaves, grass clippings, and pretty much any bio matter.

Composting toilets use the natural processes of decomposition and evaporation to recycle human waste. Waste entering the toilets is over 90% water, which is evaporated and carried back to the atmosphere through the vent system. The small amount of remaining solid material is converted to useful fertilizing soil by natural decomposition.

This natural process, essentially the same as in your garden composter by manipulating the environment in the composting chamber. 

The correct balance between oxygen, moisture, heat and organic material is needed to ensure a rich environment for the aerobic bacteria that transform the waste into fertilizing soil. This ensures odor-free operation and complete decomposition of waste.

When human waste is properly composted, the end product does not contain any pathogens or viruses (these are destroyed by bacterial breakdown). This nutrient-rich fertilizer can then be used on plants or around the base of trees, as part of the natural cycling of nutrients, reducing your need for commercial fertilizers and preserving local water quality.

A composting toilet must perform three completely separate processes:

  1. Compost the waste and toilet paper quickly and without odour
  2. Ensure that the finished compost is safe and easy to handle
  3. Evaporate the liquid

Now in saying that, composting toilets can come in many shapes and sizes ranging from a homemade sawdust toilets (which you can make from a simple bucket and a board with a hole in it) right through to major composting toilet systems like a Clivus Multrum (that can handle the needs of up to 30 people full time).

A sawdust toilet and a composting toilet are essentially the same thing, it’s just that some people look for information about sawdust toilets because they hear that sawdust is the best thing to add to a composting toilet. They are right in one sense that sawdust can certainly be used in a composting toilet, but there’s definitely other things that can be used effectively in a composting toilet.

What can you put in a sawdust toilet?

This will really depend on the composting toilet. If you’re a DIY’er and you’ve gotten yourself a 25 gallon bucket with a seat, what you can put in this type of composting toilet will differ greatly to a more elegant setup like a commercially produced toilet.

With most composting toilets, urine is caught in a separate container. Too much moisture can slow the bio-degesting process. Urine can be a good source of fertilizer on its own.

A compost pile really needs to be in the Goldilocks zone – not too cold, not too hot, not too dry and not too runny. If you find the ‘sweet spot’ then a composting toilet can be a welcome addition to any home and can operate smell free if done right.

If you’ve got a purpose built composting toilet like a you won’t have issues with excess urine as many of these options have urine diversion built in along with fans to help keep your composting pile at the right temperature and level of dryness.

How do you build a composting toilet?

This will depend on the type of sawdust toilet design you go for. If you’re going down the DIY route, there’s many different types of sawdust toilets you can make. Take a look at some of the images below to give you an idea of what you can make. The simplest toilet design is using a bucket. Seal the top with a gasket and build a small chimney so that air flow and natural convection will draw heat and moisture out of the bucket.

Many will use a 25 gallon bucket or barrel and place a plywood lid to seal the top of the barrel, attach a toilet seat with foam gaskets, and use pvc pipe to vent the holding tank upto 8-10 feet in the air to create a draft.


What happens when a sawdust toilet starts to smell?

If there’s a smell emanating out of your composting toilet then it’s fair to say “you’re doing it wrong”. Too much of anything can have an effect on your composting pile and how it works – for example, too little sawdust or peat moss in your toilet will give you an abundance of human waste when compared to sawdust.

If you’re not diverting urine, the pile can quickly turn into a sloppy mess that smells and gets full quickly.

Remember even though many people call these types of toilet systems ‘sawdust toilets’ they are in essence a composting toilet so you’re able to put a wide range of organic material in there, not just sawdust.

If you’re finding that your sawdust or composting toilet is starting to smell, why not try adding some of the following items to your pile to see if that makes a difference:-

  • Wood shavings
  • Food scraps
  • Garden clippings
  • Lawn clippings
  • Animal manures
  • Leaves and weeds
  • Hay
  • Coffee grinds
  • Straw
  • Leftovers from beer brewing or cider making
  • Shredded junk mail or newspaper
  • Rice hulls
  • Sugar cane bagasse
  • Peat moss

Are composting toilets safe?

Most definitely – as long as you follow instructions properly and keep your composting pile in working order, a composting toilet is very safe. The microbes and bacteria in the pile will break down any unwanted pathogens in the humus. This is why it’s sometimes a good idea to introduce a little dirt or other natural organic matter into your pile to help bump up the level of microbes all working to break down the pile into usable compost.

What’s the end product of a sawdust toilet?

Very simply you get what’s called humus. This is a top-soil like product that’s rich with organic materials and can be used on any garden where non edible plants are being grown. The humus can be used on fruit trees and any plant that you don’t directly eat. If done properly this soil won’t smell and is full of nutrients that plants just love.

Why not just dig a hole, or use my septic system?

If you’re wondering why people go to the trouble of installing and maintaining a sawdust composting toilet, there’s a whole bunch of different answers you could get. Some people want to live off-the-grid and make as little impact as possible to their environment. Others want to simply save water and if you have a septic system, they will need to be pumped eventually, and especially if not maintained. Some people don’t have the option of having water plumbed to their house from the mains, or rely on rainwater tanks for their drinking water, so reducing the amount of water you waste is essential.

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