A question I often get asked is “is it possible to build my own composting toilet?” The answer is yes – with qualifications. 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.
The basic home made composting toilet
A homemade composting toilet can 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. You can see an excellent video on building a simple homemade composting here.
However, it is possible to make huge improvements to this basic bucket and seat design. Below is an excellent video showing the improvements that I will discuss.
First, add ventilation. Ventilation will dehydrate the solid material and eliminate odor. The poop will rapidly shrink, greatly increasing the capacity of the bucket. No sawdust has to be added.
Attach a vent hose or plastic vent pipe to the toilet box. Run this outside, either through the wall or roof (You’ll need an external vent cap and possibly some roof flashing. The folks at the local hardware store could sort out what you need for this project). Some vents draw naturally, with the wind (you’ve seen these – they are metal, with slits, and they rotate). Or a small computer fan could be installed in the pipe. You might have to cut off the corners to make it fit. You’ll have to plug that fan into source of electricity – a wall socket or connect it to a battery. The battery can be trickle charged with a small solar panel. 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.
Second, add a urine diverting seat. Almost all odor problems relating to composting toilets result from the contents being too wet. Combining urine and solids in one tank (or bucket) is asking for trouble. The solution is to keep them separate. Buy or improvise an inexpensive urine diverting toilet seat. There will be a drain tube from the seat, which you route to a small drain pit outside of your dwelling, or send it to an existing gray water system. Or dilute the urine and use it as fertilizer. Urine has very little bacteria and does not pose a health risk.
With a urine diverting seat and a fan installed, your home built 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. You can purchase a urine diverting seat here: Privy
Finally 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 ideally 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
Keep in mind that almost all odor problems relating to composting toilets result from the contents being too wet. You could buy 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 very little bacteria and does not pose a health risk.
With a urine diverting seat and a fan installed (or rotating vent), your home built 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.
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.
For handy, do-it-yourself people on a strict budget, homemade compost toilets are an excellent solution for the difficult problem of managing human waste.