A question I frequently get asked is “is it possible for me to build my own composting toilet?”. The answer is yes. People have been building and using composting (sometimes called “mulching”) toilets for generations. However, there are a few very important things to be aware of if you are to succeed.
A homemade DIY composting toilet (or ‘do it yourself’ composting toilet) may be as simple as a 5 gallon bucket with a seat, inside a wooden cabinet. These can actually look really nice, if built by a skilled woodworker. You need to use an absorbent, natural material (like sawdust) to cover the contents thoroughly after each use. Because many home built composting toilets do not have a fan or ventilation, this sawdust cover is absolutely vital – or it will stink. A general rule is to ensure the ratio of sawdust to human waste is 1:1.
Adding a vent with a small computer fan to a DIY composting toilet would be a drastic improvement, and eliminates the need to add sawdust. If you have a square shaped bucket this would be easy. The folks at the local hardware store could sort out what you need, but essentially you want a plastic pipe installed in the rear of the toilet. This pipe is led up through the roof, where you install a vent cap (again, the hardware store people will know exactly what you need – its not complicated) . Some vents draw naturally, with the wind (you’ve seen these – they are metal, with slits, and they rotate). However, this is not as good as using a small computer fan, which can be installed where the pipe exits the box (see this video at about 2:51). You’ll have to plug that into a wall socket or battery. Another option is a solar attic vent. These are a bit pricey – maybe $200 – but they are a very nice solution, and require no wiring.
With a vent and fan, the moist, stinky air inside the toilet will be exhausted outside. The contents of the toilet will shrink rapidly, allowing much greater capacity. No additional organic material, such as sawdust, should be added. When full, the bucket is dumped into a sealed composting container on your property, where it should sit for a considerable time – 6 months to 1 year.
Keep in mind that almost all odor problems relating to composting toilets result from the contents being too wet. This is solved with an inexpensive urine diverting
toilet seat, and drain the urine into a small pit outside of your dwelling. Or dilute the urine and use it as fertilizer. Urine contains little or no bacteria and does not pose a health risk.
With a urine diverting seat and a fan installed, your home built DIY composting toilet will rival professionally built toilets in effectiveness. If you just have a bucket with sawdust, well, it’s not as good and you could run into odor problems if all users are not careful.
I’d line the plastic bucket with a compostable plastic bag, to make emptying easier.
When the bucket gets about 3/4 full, you should take it outside, and dump it in a compost bin. This should be a sealed bin, without holes in the bottom. You don’t want the contents leaching into the ground. Here it should remain, until fully composted. It might take just a few months, or up to a year, depending on the temperature. When it has fully composted, you can put it on non-edible plants as
mulch. You actually need two bins, so one can sit for the required length of time, with no new material being added. I like the rotating drums, but there are many other possibilities.
The most comprehensive book on the subject is the Humanure Handbook. You can read it free online. The only problem is that the Humanure toilet they discuss is very outdated. There are also excellent Composting Toilet Guidelines published by the BC Government in Canada.
For handy, do-it-yourself people on a strict budget, homemade DIY compost toilets are an excellent solution for the difficult problem of managing human waste.