Urine Separating Composting Toilets

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 toxic sewage.  Odor problems abound. In theory the liquid 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 seperating composting 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 separating composting toilet. These

compost toilet drain pit

typical drain pit for urine separating toilet

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 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.

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 separating composting 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 separating composting 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 separating composting 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 separating composting toilets do not have any problems whatsoever with odor – unlike some older models of composting toilets.

Still not perfect

However, even with a urine separating composting 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 store the urine in a plastic tank, and dilute it with water 10:1. It is then exceptionally good fertilizer.

If you don’t want to go that route, you can quickly 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.

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 separating composting 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. Urine diverting toilet seats are available for the handy do-it-yourselfer that wants to build their own urine separating composting toilet system.

21 thoughts on “Urine Separating Composting Toilets

  1. Hi Richard, we’re concerned that males standing to pee might experience ‘splashback’ due to the shallow urine diverter. Your advice would be appreciated, thanks.

    • You can get some splash back, if the aim is off. Then you need to wipe it, or pee sitting down. I stand up, with no problems.

  2. Here is strange question, from what I see on the Seperatt toilet, when you sit on the seat, the trap door opens up for the solids. when you sit up to wipe your butt, does the trap door close immediately? So to dispose of the toilet paper do you have to keep weight on the seat? Men can stand up and pee in it providing they aim for the front compartment correct? What stops the smell from coming back from the wet section if it is tied into the regular liquid line to the holding tanks.

    • You can do it two ways. Just put the paper in the bowl, then gently press the seat with your hand to open the trap door. Or, you can use the paper while sitting down.

      Yes, men can stand to pee. Getting a small amount of liquid in the solids chamber is not a big deal.

      The urine drains away to a pit or tank, outside the dwelling. Odor is not usually a problem. There are little minty things that can be put in that drain should you ever smell anything.

  3. I am building my own system because it is so easy to do. So as to start right away, I will be using a bucket in the bathroom, and then emptying into a covered outdoor bin. I have seen many people use saw dust as a cover material after each use. Do you know if this has any affect? Do you know anything else about or have resources for the actual breakdown process?

    Thank you.

    • I have a detailed post on this topic here: build your own composting toilet

      Sawdust is the way to go when building a toilet yourself. A layer of sawdust will contain odor and prevent flies. Use a ratio of sawdust to poop of 1:1. I have heard anecdotally that aged sawdust, already starting to rot, works better. The type of sawdust matters. Sawdust from some woods, like cedar or teak, do not rot quickly enough. The Humanure Handbook has a very thorough discussion of homemade compost toilets.

      I strongly suggest you find a way to divert the urine. Combining urine and solids in one bin can create a very smelly toilet! Diverting the urine will make everything much easier for you.

      Sawdust is not usually required in commercial composting toilets, which contain the waste in a sealed, gasketed chamber and exhaust any odor outside with a fan.

  4. I am thinking about buying one, but wondering how it works to divert urine if your average visiting 8 yr old boy doesn’t know to ‘aim forward’ in the bowl–in other words can it be used by folks not used to them and not get too much urine in the ‘non-diverted’ part?
    Thanks for any info!

    • If a small amount of urine goes into the main chamber, that is ok. The toilet can definitely cope with that. One does not need to aim at the small opening – just aiming towards the forward section of the bowl should be fine. There is a little dam there – you can see it in the photos, that ensures liquid in the forward part of the bowl will drain forward. However, you should definitely tell all male users to pee forward. If they are too young to follow instructions, then you need to use the child’s seat, with comes with the toilet.

  5. Richard, thanks for all this information!

    I am curious — what about toilet paper? Surely, that would add to the bulk significantly, as paper is not 90% water.

    Another question I have is on using Separett at lower temperatures. I am considering Separett for a cottage I use on weekends. It is currently equipped with an old Incinolet — quite a production to use that one! In wintertime, I keep the cottage around 50 degrees during the week, while I am not there. Winters in Catskill Mountains of NY can be quite cold, so I am just trying to avoid frozen pipes. Will this affect the toilet in any way? In theory, colder drier air this should help the drying of the stuff inside, but I did want to confirm.


    • Toilet paper is not a problem. It compresses very well. You gat 60-80 “uses” before you need to empty, and this allows for the toilet paper.

      Cold weather is fine. The main composting takes place later, after the bin is removed. If you store the removed bins in a cold place, composting will be suspended until it warms up.

  6. I have a home with two bathrooms and was not pleased with the composting system that was in place. Reading about the Separett, I felt it was worth a try. I installed one on a trial basis, but after a year, readily installed another in my second bathroom as well. This unit is simple to install, sturdy, quiet, and completely reliable. Maintaining it is snap. I would recommend this unit without reservation. In case anyone is interested, this is used in our year-round home, not just a summer cabin.

    Bob Andrews
    Craig, Alaska

  7. What kind of building permit/approvals are generally needed to install a Separett in a city. I’m looking at a small house in Longmont, Colorado, which has an outbuilding that would make a great studio/workshop. I’d like to have a toilet in the studio, but I don’t want to go through the expense of extending the sewer line. The only issue I can see would be the french drain, since everything else is self-contained. Do you know if this is a problem?

    • Regulations vary widely, and I do not know about Longmont, CO. However, there is usually nothing illegal about putting a composting toilet in a room and using it. Basically it’s a fancy bucket. Now if there was no other plumbing option in the house (ie a regular flush toilet) they might disapprove. People install them in out buildings all the time.

      In my area the officials say “don’t ask, and we won’t say no”. The inspectors realize the rules were made before composting toilets became common. Hopefully, they have the same attitude in your area.

  8. Several questions: (a) You indicate that the feces will break down on its own. There is no need to add dry organic material at all while the bucket is in use? It’s just a big, ever-aging pile of feces? (b) In the Separett video, it shows a white pad being placed in the liner of the bucket. What is that for? (c) I’m considering this for a cottage in the north, that gets used pretty much only in June-September. The first freeze will come some time in October, usually. What’s the best way to handle the solids – can the last person to use it just put the bucket outside in a non-insulated shed, and not worry about it until spring? (I’m assuming it’s better to have it out of the weather.) (d) How does one clean this after each use?
    Many thanks -

    • Feces is almost 90% water. With liquids being diverted (or evaporated, depending on the toilet used) you have fairly dry, crumbly contents. It breaks down and shrinks very quickly, and you do not have a “pile of feces”. In fact, if you can wait a few days after the last use before opening it, you probably will smell nothing.
      The pad is to absorb extra moisture. I’d say that is not necessary.
      Composting will slow down in cold weather. You can remove the bucket and put it in the shed when you leave at the end of summer, or let it sit until spring – no problem either way.

  9. I am intriqued by the Separett toilet, but you failed to mention that the composting of the feces is done after the contents are removed from the toilet and taken outside in a bag. How do you accomodate 5 or 6 buckets of feces sitting in your garden at any given time waiting to be composted and emptied onto a garden? Would not a compost bin be better? Neighbors would complain, you know. Seriously wondering. Thanks!

    • Good questions. You will be relieved to know there would not be “5 or 6 buckets of feces sitting in your garden”. (That would be awful!). The solid material begins drying out and breaking down almost immediately in the Separett. This happens very rapidly. In as little as one week, any solids will be dry and odor free. When you open it, say 2 or 3 months after installing it, the older contents have almost entirely broken down. The very recent additions of solid material will not have broken down, obviously. But it is not like opening a container full of fresh poop – nothing like that. If you can avoid using it for a day or two before opening, you probably won’t smell a thing.

      Then you remove the inner composting bucket (lined with a compostable plastic bag), already containing well dried out, broken down material (mostly), and put the lid on it. You can put a layer of sawdust or other organic material on top. It is important to note that there should be no odor whatsoever at this stage. This has to sit for 6 months, to eliminate the possibility of any remaining pathogens. Then you still only put it on non-edible plants, and do not mix with compost for your vegetables. This is just to be absolutely sure. You can’t be too careful with human waste.

      The beauty of the Separett is the massive capacity. Because no liquids enter the chamber, the solid material shrinks, breaks down and dries out rapidly. Many people report they only empty once every 3 or 4 months. It comes with 3 “bins” that you rotate. So capacity is essentially unlimited.

    • Good news. You can now purchase the Separett toilet through me. I was so impressed with this design, I became a dealer. Here is the page: Separett

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