Composting Toilets, an Introduction

(Updated 12/12/2011)
For additional information, see our other web pages on composting toilets:
-Composting Toilet Regulations
-Bucket-to-Barrel Composting Toilet
-Barrel Composting Toilet

Composting toilets are simple, low-tech, waterless toilets. They are designed to provide favorable habitat for biological agents of decomposition such as bacteria, mold and fungi which break down feces and urine into compost. This miraculously transformative process encourages us to move beyond the concept of mere "waste disposal". It opens an opportunity to use our own compost to grow food for ourselves and thus to close the nutrient cycle. As such, using composting toilets can be a step toward relearning our place in the natural order.

We have been using composting toilets since 1990, using the resulting compost to grow a variety of edible plants.

Since most aspects of composting toilets including design, use, legalities, etc. are addressed in the several books listed at the end of this section, I will cover them only briefly here. During 16 years of designing and using composting toilets I've observed some details which have not been covered extensively elsewhere. These are the primary focus of this section. Since composting toilets require little if any water, they are especially appropriate for use in aridlands and particular attention is given to that aspect here.

First, though, I'll cover the five primary factors necessary to create habitat favorable for the biological agents that destroy pathogens and convert feces and urine into compost. They are nitrogen, carbon, oxygen, temperature and moisture. Problems with composting toilets can often be traced to significant imbalances in one or more of these factors.

Nitrogen is required for microbial decomposition and is present in human feces and especially in urine. No additional nitrogen needs to be added to a composting toilet.

Carbon is also required for microbial decomposition and ideally should be in a proportion of about 30 parts carbon to 1 part nitrogen. This ratio can vary considerably without seriously affecting decomposition. Carbon is supplied by adding a carbon-rich material to the compost. Suitable carbonaceous material includes sawdust, straw, leaves, shredded paper, etc. Shredding or chopping these materials provides greater surface area for the decomposition organisms and also facilitates the absorption of moisture. Whatever the type, this carbonaceous material is often referred to as "bulking agent" although I prefer "cover material" as it emphasizes the aesthetic function described below.  For more information on cover materials, see our Cover Materials webpage.

Oxygen, also necessary for decomposition, is provided either through mechanical means (stirring or tumbling) or by adding coarse carbonaceous cover material which provides air spaces throughout the compost.

The temperature of the composting chamber should ideally be in the range of 80F to 110F, although the temperature of the compost itself may be higher, depending on the type of microorganisms that predominate. Although low ambient temperatures will slow down or even stop the process of decomposition, it will resume when the temperature rises.

Moisture is also necessary for decomposition and should ideally be about the same as that in a wrung-out sponge. One of the most common causes for poor decomposition in composting toilets used in aridlands is lack of sufficient moisture distributed uniformly throughout the compost.


Attention to aesthetics makes using the toilet a pleasant experience for everyday users. It also challenges the preconceptions of guests, many of whom approach composting toilets with trepidation, expecting the unpleasantness often associated with outhouses such as seeing exposed excrement and toilet paper when the lid is lifted. In fact, it should be no more necessary to have to look at someone else's excrement or used toilet paper when using a composting toilet than is the case when using a flush toilet.

Many commercial designs attempt to resolve this aesthetic issue by segregating the user from the composting chamber, either by some type of moveable baffle or by a long chute between the toilet seat and the composting chamber. Baffles are prone to jamming and chutes to unsightly "skid marks" (black chutes help but don't entirely solve the problem).

Our preference is for simple toilet designs that rely on a modicum of skill and care in use rather than on technological gizmos. Here are three easy steps that we use to resolve the aesthetic issue:

First, to facilitate complete covering of ones deposit, we keep a squirt bottle of water beside the toilet for the purpose of wetting down the used toilet paper. Wetting reduces the volume of the toilet paper and allows cover material to adhere to it better. This makes covering the used toilet paper much easier and requires less cover material to be used. An old liquid detergent bottle works well for this. Less than half a cup of water is required per use.

Second, we use cover material for an aesthetic as well as a biological function, sprinkling enough cover material over toilet paper and feces to cover them completely so that the next user sees only cover material.

Third, over time, feces, toilet paper and cover material will build up in a mound directly under the toilet seat. (This does not tend to occur with bucket toilets.) This makes the covering of ones deposit more difficult since feces and toilet paper tend to fall down the sides of the mound and spread out over the surface of the composting chamber. The mound should periodically be leveled off. Although a hoe or stick can be used for this job, a more effective tool is an inexpensive garden cultivator, the kind that looks like a miniature pitchfork with the tines bent at a right angle to the handle. To further facilitate the covering of deposits, it's a good practice to go beyond simply leveling the surface of the compost pile to actually hollowing out the area under the toilet seat so that feces and toilet paper land in a depression. Covering ones deposits is then much easier. After leveling or hollowing, cover any exposed feces or toilet paper with cover material.

Finally, we've found that keeping the toilet clean often makes acceptance easier.


A clean toilet makes for a happy user!


Insect Control

Insect control is another neglected aspect of compost toilet design and use. Few commercial composting toilet designs feature effective insect control. A composting toilet is a micro-ecosystem that favors biological agents of decomposition.  It is also an excellent reproductive habitat for a variety of insects and other arthropods such as flies, gnats and mites. Regardless of how insect-proof the composting chamber is, or how religiously the toilet seat is closed after each use, these organisms will enter in various ways including flying or crawling in when the seat lid is open or by being embedded in cover materials. By whatever route, periodic insect infestations are likely to occur, resulting in mere annoyance if gnats or mites enter the home when the toilet is used, to potential disease vectors in the case of flies, which are also attracted to human food. Infestations can, to an extent, be prevented by avoiding cover materials such as leaves that may provide a conduit for these organisms. Nonetheless a more effective solution is necessary and often overlooked.

Insect trap


Insect trap with parts laid out

When we first began using composting toilets, we occasionally experienced insect infestations. Eventually, we developed the insect trap described here and it marked the end of insects as a significant problem in our composting toilets. The trap is simple, consisting of a transparent container with a funnel at one end through which insects enter, attracted by light passing through the container and into the composting chamber. The funnel is oriented such that the insects can enter the jar easily but find exiting difficult. Success of the design depends on a composting chamber that is insect-proof and in which light enters the chamber only through the insect trap.

We have had excellent results building insect traps using one gallon wide mouth jars with a hole cut in the lid. A funnel is made from the top of a 2 liter clear soda bottle. The funnel is placed in the mouth of the jar, the lid is screwed on and the mouth of the jar is inserted into  a hole near the top of the composting chamber. If the toilet is outdoors, the trap should be on the south side (in the northern hemisphere, that is) to maximize the sunlight entering the trap. Painting the bottom half of the trap black will cause it to heat in the sunlight, killing the trapped insects. If the toilet is an indoor design, some low-wattage bulbs such as LED's should work well for the light source. We've also had good success using 1 quart canning jars and rings and making the funnel from small clear soda or drinking water bottles.  

Using Composted Human Feces for Growing Food

Whether to use composted fecal matter to grow food is largely a matter of judgment. If you are new to composting, or have any reason to doubt whether your compost is pathogenically safe, it is prudent to use it only for fertilizing plants in which the edible portion is well off the ground, such as fruit or nut trees.

At the other end of the spectrum, we have for many years used the compost from our composting toilet, which is well managed and is used almost exclusively by us, for fertilizing our vegetable garden and have done so with excellent results.


Screening finished compost


Enjoying finished compost!

Applying finished compost to garden


Completing the nutrient cycle!

Some of My Previous Composting Toilet Designs...

Featured below a few of the composting toilets I've designed over the past 15 years. With the exception of the first design, all are "batch" type toilets in which feces, urine, etc. are collected in a chamber for a period of time. That chamber is then left to age while another chamber is filled. This prevents contaminating aged compost with fresh material.

The first three designs were built in south Texas. They featured drains to small subsurface seepage pits for draining excess leachate (urine). They would have benefited from insect traps, which we didn't develop until moving to Arizona.

For a description of the systems we're currently using, see our Bucket-to-Barrel Composting Toilet page and our Barrel Composting Toilet page.



My first composting toilet. It was designed for one person in fulltime use and featured a drawer in the bottom for removing compost.



Delicious papayas irrigated from the leachate drain!




Toilet for 1-2 people in full time use. Built of 3/4" plywood covered with epoxy.



Top open for emptying compost.

Interior view of compost chamber.


A larger version of the 2 chamber design above, sized for a family of 4. The composting chambers extend out through the wall with access doors for emptying outside. Also built of 3/4" plywood, covered with epoxy inside the chambers and finished with formica. This toilet was permitted by the county on a pilot-project basis.


Outdoor composting toilet...

...showing composting chamber...

...and rear view - note insect trap below vent.


The is a toilet we used for many years at our homestead in Arizona. It's the first outdoor toilet I designed. It is well adapted for our desert climate as the subterranean composting chamber conserves moisture well. At first glance, this composting toilet is reminiscent of an outhouse. In use, it is very different. Absent are the flies, odors, and repulsive slurry associated with outhouses. Below the toilet is a composting chamber which is simply a circular hole in the earth 3 feet deep and about 3 1/2 feet in diameter. The hole is lined with layers of hardware cloth to prevent the sides from caving in.

Two people using the toilet full time filled the chamber in about a year to a year and a half. When the chamber is full, the toilet is slid over a second chamber and the process is repeated. As the second chamber is being filled, the contents of the first chamber are turning into compost. At the end of the second year, the process is repeated.



Bucket toilets

Note: One of the composting toilet designs we are now using is a modification of this system, described on our Bucket-to-Barrel Composting Toilet page.



(Above) Composting bins for bucket toilet

(Left) Simple 5 gallon bucket toilet with snap-on seat from camping supply store

(Above) A more elaborate wood cabinet with bucket of sawdust cover material beside.


(Right) Same cabinet with lid open.



The bucket toilets pictured above are about as simple as composting toilets get. A bucket is used as a toilet receptacle with sawdust used as a carbonaceous cover material. When the bucket is about 3/4 full it is carried to an outdoor composting bin where the contents are deposited. The bucket is then rinsed and reused.

I experimented with toilets of this type in the early '90's and have recently returned to the concept for its simplicity and replicability. In the interim, Joseph Jenkins popularized the bucket toilet in The Humanure Handbook. For the past couple years, we have been experimenting with adapting the bucket toilet to our desert climate. The first version shown above is just a 5-gallon bucket with a camp-style snap-on toilet seat set outside under the shade of a mesquite tree. (No need for reading material - watching the desert is entertainment enough.) Many of our visitors see it and exclaim, "This is something I could do." The obvious simplicity of design belies the greater skill and care required to use it well. For this reason, I am including more detail about its use, especially in aridlands.

For the composting bin part of the bucket toilet system, we have experimented with various bins from pits dug in the ground that cost nothing, but were at an inconvenient height, to above-ground cylinders of hardware cloth that were easy to build and were at a convenient height but permitted the compost to dry out too quickly.

Making compost bin of galvanized roofing panels

Bin of polycarbonate panels also showing carpet compost cover


We are currently experimenting with bins of corrugated galvanized roofing panels and also polycarbonate plastic, both available at building supply stores. The galvanized panels make a stiffer bin, but may corrode over time... we'll see. The idea behind the impermeable bins is two-fold. They help to conserve sufficient moisture for composting in this arid climate and, being slick-sided, they prevent rodents and other small animals from gaining access to the compost (the latter has not been a problem, but as it's a concern to health authorities, this feature may bring them a step closer to considering this type of toilet.)

We find that bins about 3' high and 5' in diameter are a good size for two or more people and are about as large as one would want to use. 3' is a convenient height for most people and if the diameter is more than about 5' it becomes difficult to reach the center when dumping the bucket.

Another aridland adaptation is a piece of indoor/outdoor carpet covering the compost (as pictured above, right). This serves several functions: it helps prevent compost from drying out, it provides an additional insect barrier and it helps prevent leaching of rainwater through the compost during thunderstorm downpours.

Insect vector control is as necessary with bucket toilets as with any other type of composting toilet. Instead of using insect traps though, insect control is accomplished through the use of cover material as described below. In hot climates, coarse cover materials that permit insects to access the moist interior of the pile where they can breed should be avoided. During the hot months, we've found that a cover over the compost of 6 mil black plastic sheeting, weighted around the perimeter with fist sized rocks, works well. The black plastic becomes quite hot in the sun, discouraging insects from laying eggs in the compost.


Black plastic bin cover weighted down with fist-sized rocks.


Sawdust bucket beside toilet bucket


Chopped straw for bin cover material

For covering one's deposit after using the bucket, the ideal cover material is clean and absorbant and has a pleasant fragrance. Since the cover material also serves as the insect barrier in this type of toilet, it should be fine enough to prevent insects from gaining access to fecal material. For these reasons, sawdust makes the ideal cover material for bucket toilets. It is important that deposits are completely covered after each use. Follow the cover material procedure in the "Aesthetics" section above, except note that it is also for insect control in bucket toilets.

Sawdust can often be had for free at lumber yards, cabinet shops, mill works, etc. Be sure to ask if the sawdust contains pressure treated lumber or glue and if so, avoid it.

When the bucket is emptied into the composting bin, its contents should be immediately covered. The ideal cover material for this is something coarse enough to form air spaces in the compost yet fine enough to prevent insects from gaining access to the fresh fecal matter that has just been deposited on top of the compost. An excellent material for this is chopped straw. It decomposes at about the same rate as feces, it is coarse enough to provide air passages, yet fine enough to prevent insects from gaining access to feces. Enough straw should be used to completely cover the fresh deposit so that insects cannot gain access to it.

Straw can be purchased at most feed stores and is easily chopped using a chipper/shredder machine. It should be stored in a dry location because if it gets wet it becomes lumpy and difficult to use.

Dumping the bucket is the crux of this method. It sounds simple, but making an enjoyable job of it requires developing a routine. Here's how we do it...


1) Ready to dump bucket - brush and squeeze bottle handy


2) Dumping and slapping side of bucket to empty sawdust sticking to inside

3) Rinsing inside of bucket - rinse water dumped onto pile


4) Brushing off "skid marks"

5) Final rinse - total of 1 pint water used


6) Setting down bucket to dry

7) Covering bucket contents with chopped straw

8) Flattening out straw-covered bucket contents with hoe


9) Final covering with chopped straw


10) Done! Elapsed time - 5 minutes


The impermeable sides of this desert-adapted composting bin, which do such a good job of conserving moisture, also prevent air from entering the compost through the sides, so the compost should be aerated occasionally. Using a pitchfork, we fluff the compost about once a month. This is a 10 minute job and one of my favorite homestead activities--it's always interesting to see how the compost is progressing.



Recommended reading:

--Lifting the Lid by Peter Harper and Louise Halestrop

--The Composting Toilet System Book by David Del Porto and Carol Steinfeld

--The Humanure Handbook by Joseph Jenkins


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