Composting 101

There is nothing difficult about composting human waste. It does require a small amount of knowledge, and occasional monitoring. There is a link to an excellent article on the topic below, but in a nutshell…you need two bins. Use one only at a time. When the first one is full, start using the second one. When the second one is full, the contents of the first should be ready for the non-edible plants. When I put waste in my composter, I like to cover it with dry grass or leaves, but that is optional. It breaks down very quickly, and there is never any odor. It should NEVER get wet or slimy. If it’s getting wet, you need more dry material. It should never dry out. If it’s getting dry, add a little water. Please see the detailed article at 

How to prevent flies in composting toilet

A question that comes up from time to time is “I have flies (or gnats or whatever) in my composting toilet. How do I get rid of them?” In my experience, about one person in 20-30 eventually has this problem, so you are not alone. The good news is, you can easily get rid of flies and dramatically reduce the chance of getting them again.

The first step is to eliminate potential sources of flies in the home. The toilet does not produce flies, and there should not be flies or fly eggs in human waste. That means the flies came in from somewhere else. Fruit bowls are a big culprit. Once in the home, flies will be attracted to the toilet, where they lay eggs and multiply. Before leaving your cottage, eliminate all possible sources of flies, including garbage (not even an apple core should be left behind) or compost.

Natures Head fan housing is easily removable

Natures Head fan housing is easily removable

The second thing you do is make the toilet unattractive or unavailable to the flies. Clean the toilet very well inside, in every nook and cranny, with something that will kill fly eggs like a mild bleach solution. Water and vinegar will not work. Don’t get the fan wet. With the Nature’s Head you can remove the fan housing and hose it all down outside, after using the bleach. However, the Separett fan housing is a bit of work to remove, so it’s best to clean the toilet with the fan housing in place.

diatomaceous earth for composting toilet

diatomaceous earth for composting toilet

Add about 5 cups of diatomaceous earth to the new coconut coir in the Nature’s Head, or with the Separett add a cup per week to the removable bucket. You may have to experiment a bit for the optimal quantity.  Diatomaceous earth is a naturally occurring, soft, siliceous sedimentary rock that is easily crumbled into a fine white to off-white powder. It is a very good natural insecticide. This will solve the fly problem 99% of the time. It is not expensive and commonly available.

Be sure the fan screens are clean, unobstructed, and pumping air. You should be able to feel air being blown out at the exhaust vent.

moth cake for composting toilet

moth cake for composting toilet

As a very last resort, you can put a small “mothball cake” in the lower part of the toilet. The fan should exhaust the odor, and you should not smell mothballs in your home. This will definitely stop all flies. However, mothballs contain a chemical insecticide, and therefore must be used cautiously.

Once you do these things, I am quite sure you will have no more fly problems. Cleanliness and removing the source of flies is by far the most important step.

Nature’s Head Review 2

The Nature’s Head has worked great! I have a 30′ Pearson sailboat. The holding tank was way too small and took up room in what would have been a wet locker. It always smelled. It is illegal to pump over board and the pump out stations were not functioning most of the time . With four people on a 3 day weekend the holding tank would soon be overflowing. I looked at replacing the holding tank for a larger size but that reduced space further. I then started looking at composting toilets. The short answer is the first season in Maine the toilet worked like a charm. It doesn’t smell. It was simple to install and I was able to use the composting portion for the whole season with about every weekend use and a week family vacation with at one weekend 7 people on board! Urine disposal is quick and easy. It fits great in a cloth grocery bag and you simply dump it at the marina toilet. The only addition I am going to make is add an extra urine tank as we moor at islands that do not have marinas. The product works like a charm and I don’t have to worry about what my kids are swimming in.

Separett Toilet Review

Separett Composting Toilets

Separett composting toilet
Separett Villa

Separett composting toilets are only now becoming widely known in North America, although they have been used and proven in Europe for over 10 years. These are “urine separating” toilets, which divert the urine away from the main composting chamber for separate disposal.

The logic behind this is simple – most of the problems associated with composting toilets result from too much liquid in the composting chamber. If there is too much liquid you can get odor problems and leaks. Composting will not occur if the contents of the main chamber are too wet. Instead of compost, you get a tank full of sewage.

Separett composting toilet urine drain forward
top view showing separate openings for liquids (forward) and solids.

The older composting toilet designs try to get around this problem with evaporation. They use built in electric heaters and/or fans to achieve this. As long as evaporation can keep up with the liquids being introduced, this will work fine. But in the real world, they sometimes fail to keep up, and the aforementioned problems occur.

Separett composting toilet drain pit for urine




By eliminating urine at the source, Separett toilets avoid these problems. However, you do need to devise a method to get rid of the urine. Separett suggest diverting it directly into a simple drain pit outside of your home or cottage. Alternatively you can store it in a tank, dilute it 10:1 with water, and use it as fertilizer. A third option is to connect it to your gray water system. Urine is basically sterile and does not pose a health risk.

The Separett toilets come in two models – the 9200, which plugs into a regular wall outlet or the 9210, which runs on 12 volt electricity (i.e. battery, solar panel). An adapter is included with the 9210 so you can actually plug it into a wall if your needs change.

Separett composting toilet emptying
sliding out the removable bin (shown with lid on)

Striving for simplicity (which equals greater reliability and lower cost), there are few moving parts inside the Separett. Unlike many other toilets, there is no mechanical system to rotate the contents, no trays that must be cleaned, no drawers that slide out, and as mentioned, no heaters.

The Separett uses a removable composting bin, lined with a compostable plastic bag, to contain the solid wastes. The company states that, because very little liquid enters the bin, it should not need to be emptied frequently – but this depends on how many use it. Practically speaking, a family of four would likely empty it once every 2 months or so.  When the bin becomes full, you open the toilet, close the compostable plastic bag, and roll out the inner composting bin. The Separett comes with three of these inner bins, so you simply replace the full one with an empty one. Put the lid on the bin you just removed, and let it sit somewhere for about 6 months for the contents to fully break down. After 6 months, it is safe to put the contents on ornamental plants.

A big advantage of the Separate is that the inside of the toilet itself stays clean. All waste is contained in the compostable bags and removed. You are never faced with cleaning composted, semi-composted and (yuck) un-composted feces from inside the toilet. This is a common (and unpleasant) task with older styles of composting toilets.

Separett composting toilet inner bin
removable bin lined with compostable bag

With the three included composting bins, the Separett has essentially unlimited capacity. You can purchase extra bins if large numbers of people are using the toilet.

One nice feature is the weight activated “door”. The lower chamber remains tightly sealed at all times, but once you sit on the seat the door automatically opens, allowing solids to drop below.

The Separett is an attractive toilet that would not look out of place in any home. There is no awkward step up, as with some models. It seems well made and sturdy. There are no complex inner workings, like mechanical “raking” systems that are prone to failure. There is a 5 year warranty. Separett is made by well paid and fairly treated workers in Sweden, which makes the very reasonable price surprising.

Separett composting toilet inside, bin removed
Inside the toilet, bin removed

See a detailed installation video here.

Urine Diverting Toilets

Urine diverting toilets are a significant improvement over older composting toilet designs, that combined urine and solids together in one tank. They eliminate most of the moisture in the toilet, substantially reducing odor, and making the break down of solids much easier.
drain for Separett urine diverting toilet

Drain for Separett urine diverting toilet – simple!

Although most composting toilets work fine when properly installed and operated, I do frequently hear complaints from people who say their toilets “are not working” or that they simply smell bad.

The main problem is usually too much liquid from urine. If the contents are too wet, you will not get compost. You will get a sodden, stinking mass of sewage. Odor problems can certainly occur. In theory, the urine should be evaporated by the built in heater and/or fan. But in practice, the volume of liquid may simply be too great for this to be accomplished. Emptying a toilet full of un-composted material is hard to even think about.

To try and solve this problem, many non urine diverting toilets have overflow drains to handle excess liquid.  These drains MUST be clear and working properly. The overflow drain must be led somewhere below the toilet itself so gravity can cause it to flow away. That may be difficult, especially if you are already at ground level or don’t want to cut holes in your floor. Also, you need a sump, container or pit where this excess urine can be stored. If you have a properly working overflow drain, you should have no problems. The overflow will be urine mixed with feces, so it cannot go into the gray water system. It cannot be drained into a pit, and it cannot be used as fertilizer. In other words, it’s a problem.

A better mousetrap?

A superior solution in some ways is a urine diverting composting toilet (also called a urine separating toilet). These have only recently become more widely known. You use the toilet normally, but most of the urine is diverted automatically into a separate container. This means the solid contents remain only slightly moist – perfect for composting. Separating the urine solves the excess liquid problem common to most conventional composting toilets. The urine has not been contaminated with feces, so in many areas it is legal to send it into the gray water system. Typically, this will be a tube running from the urine diverting toilet to the drain below the bathroom sink. Or you can store the urine in a tank, dilute it with water, and use it as fertilizer. It can also simply be led into a small drain pit beside the dwelling.

urine diverting toilet drain pit

typical drain pit for urine separating toilet

According to the group SOIL (sustainable organic integrated livelihoods) – a non-profit that builds composting toilets in Haiti – urine diverting toilets are the way to go.  They have experimented with many different methods. From their website:

“Urine Diversion toilets have the significant advantage of reducing the amount of waste that needs to be transported therefore reducing gasoline consumption and costs. Because the excreta remains dry, the toilets are also less odorous than other toilet models and very pleasant to use.”

Other advantages

Another advantage of the urine diverting toilet is that no heater is necessary. Some composting toilets made by Envirolet, Biolet and Sun-Mar use heaters of up to 500 watts. That could be a significant cost, with our soaring energy rates. And what is the point of installing a “green” toilet if you use large amounts of electricity to run it? The heaters may eventually fail, costing more money. All manufacturers do have non-electric or 12 volt models, which use little electricity. However, you must be extremely careful to have a working overflow drain in those non-electric toilets.

Urine diverting toilets need only a small, inexpensive, easy-to-replace fan that uses very little electricity. Or they can be hooked up to a solar vent and you can forget about the fan and power use entirely.

Solid human waste is approximately 85% water by volume. This means that a urine diverting toilet will have enormous capacity for its size. The solid material dries out and shrinks dramatically (just like a compost pile in you backyard).

And finally…urine diverting toilets do not have any problems whatsoever with odor – unlike some older models of composting toilets.

Still not perfect

However, even with a urine diverting toilet you still need a way to dispose of the urine. Fortunately, this is fairly easy. Urine is sterile and does not pose a health risk.

The easiest solution is to run the urine drain into the gray water system. If you don’t want to go that route, you can build a simple “French drain” to solve the problem. This is a small pit, about 2′ wide and 2′ deep, filled with small rocks. You cover the rocks with landscape fabric and place soil and grass seed on the top.

Run a tube from the toilet, through the wall or floor and directly into the French drain adjacent to the building. This way you will never have to think about the urine again, as it is getting disposed of constantly.

You can also store the urine in a plastic tank, and dilute it with water 10:1. It is then exceptionally good fertilizer.

Many people install the smaller urine separating composting toilets on boats and in RVs. In this case, the urine can be dumped in any conventional toilet or outhouse as needed.


Some urine diverting toilets, such as the Nature’s Head, are smaller, self contained units suitable for 2 people full time or weekend use for up to 4 people. The larger Separett toilets have more capacity and are suitable for a family and general household use. Either toilet will be emptied about once every 4-5 weeks with full time use. This takes between 2 and 3 minutes, and is not unpleasant. Unless you have just used the toilet, there will be little or no odor when you empty it. Urine diverting toilet seats are available for the handy do-it-yourselfer that wants to build their own urine diverting toilet system.

Price comparisons

This is a US price comparison of self-contained composting toilets. Prices change, companies have sales – so please confirm current prices with dealers for these products before you order one.

Toilet Basic price Shipping Total
Nature’s Head $925 $35 $960
Separett 9200 or 9210 $1389 Free shipping $1389
Envirolet MS10 $2439 (but goes on sale for about $1900). Includes a passive wind vent (worth about $50) $139 $2039-$2578
Sun-Mar Excel $1790 You pick up $1790
Biolet 10 $2399 (goes on sale for 1899). free $1899

Note: The above toilets have important differences.  The Nature’s Head and Separett are urine seperating designs, while the Envirolet, Sun-Mar and Biolet combine the urine and solids. The Nature’s Head is a somewhat smaller toilet, and suitable for up to 2 people full time. The Biolet 10 is rated for 3 people. The Envirolet is rated for up to 8 people, the Sun-Mar Excel 3-4 people, and the Separett has unlimited capacity. (That is because the contents are removed from the Separett, in a compostable plastic bag, to complete the composting process in a secondary container).