A composting toilet is a waterless toilet that collects urine and solids separately. That separation is the key: smell mainly comes from poo and pee mixing, and as long as you keep them apart and cover the solids with dry material, the toilet barely smells at all. One thing worth knowing up front: nothing really composts inside the toilet itself. The toilet collects and keeps things dry, and the actual composting happens later on a separate compost heap. For a garden shed, tiny house, boat or off-grid spot it is a solid solution, as long as you sort out proper ventilation and know what you are going to do with the contents.
In this guide you will read exactly which types exist, which toilet suits your situation, what it costs to buy or build yourself, how to install and vent it, which cover material works, and what you are allowed to do with the urine and the solids in the end.
What is a composting toilet and how does it work?
A composting toilet, also called a dry toilet or separating toilet, works without flush water. At the top of the bowl sits a separator: a moulded insert with a channel at the front for urine and a larger opening at the back for solids. The urine runs through a hose into a separate jerrycan or tank, and the poo drops into a bucket or container underneath.
After every number two you throw a scoop of dry cover material over the solids. That absorbs moisture, covers everything up and keeps insects and smell away. A fan or vent pipe carries moisture and any odour outside.
The term “composting toilet” is actually a little misleading. No compost is created in the toilet itself. There is too little space, too little time and not the right environment for real composting. The toilet keeps things dry and low in odour. Only when you move the solids onto a separate compost heap and let it mature long enough do you get usable compost. That distinction matters, because it determines what you do next and what to watch out for (see the section on composting further down).
Why does separating work so well against smell? Fresh urine is virtually sterile, and dry solids under a layer of cover material barely smell. That typical toilet stench only appears when urine and faeces start fermenting together and ammonia is released. Manufacturer Separett states that separation can reduce odours by up to around 80 percent (Separett).
Which types of composting toilet are there?
There is a big difference between a simple bucket box and a luxury model with a fan. The main variants:
Separating toilet with no outlet and no power (basic dry toilet). A box or bowl with a separator, a urine container and a bucket for the solids. No electronics. Cheap, reliable and ideal for a DIY build. It does ask for discipline with the cover material and regular emptying, and works best with a passive vent pipe.
Composting toilet with an electric fan. Same principle, but with a 12V or 230V fan that continuously pulls air out through a pipe. This keeps the solids dry and the room odour free, even with heavy use. Brands like Separett and Trobolo work this way.
Model with a stirring mechanism. Best known from Nature’s Head. After use you turn a handle that mixes the solid mass with coco coir. This spreads the moisture and delays odour, but it still does not truly “compost” inside the toilet.
Urine diversion versus a collection container. Some toilets drain urine straight outside through a hose or into a tank (urine diversion). Handy in a fixed location. In a tiny house or on a boat you usually go for a removable urine container that you empty yourself.
Incinerating toilet. A completely different principle. This toilet burns the contents at high temperature, leaving only a small amount of ash. Cinderella is a well known brand. It needs plenty of power (electric models around 1500 to 1800 watts for a few minutes per burn) or gas, and costs considerably more than a composting toilet (Camperland). No compost, but plenty of convenience.
Chemical toilet (cassette toilet). For completeness: the classic Thetford style camper loo mixes everything in one tank with a chemical fluid that binds odour. You have to empty that tank at a designated disposal point and keep buying chemicals. A composting toilet uses no water and no chemicals, and separates instead of mixes.
Composting toilet, incinerating toilet and chemical toilet compared
| Feature | Composting toilet | Incinerating toilet | Chemical toilet |
|---|---|---|---|
| Water needed | No | No | Yes (flush water) |
| Chemicals needed | No | No | Yes |
| Power needed | Only for the fan (very little) | A lot (or gas) | No |
| What is left over | Urine + solids for compost | Small amount of ash | Full mixed tank |
| Emptying | Yourself, into your own compost/garden | Throw the ash away | Take to a disposal point |
| Purchase price | Low to mid | High | Low |
Which composting toilet suits my situation?
The best choice depends on how often you use it, whether there is power and how much space you have. This table will point you in the right direction.
| Situation | Recommendation | Why |
|---|---|---|
| Garden shed / allotment | Basic separating toilet or a DIY build with a vent pipe | Light use, often no power, close to the compost heap |
| Tiny house (permanent) | Composting toilet with a 12V fan | Daily use calls for good extraction and dry solids |
| Boat | Compact model with a urine container, 12V fan | Little space, no black water discharge wanted |
| Camper van / holidays | Compact portable separating toilet | Light, no chemicals, easy to empty on the road |
| Off-grid home | Composting toilet with a solar powered fan | No water connection, low energy use |
| Emergency / temporary | Bucket with a separator and cover material | Quick to set up, cheap |
A useful reference point when estimating capacity: Separett states that the solids container of the Villa suits roughly 4 people for around 2 weeks, and that the compact Tiny, used by two people, needs emptying about weekly for the solids and pretty much daily for the urine container (Separett Villa). So do the maths for yourself: the more people and the heavier the use, the more often you empty.
Buy ready made or build it yourself?
Both work fine. The difference is in convenience, looks and price.
Buying ready made. You get a finished toilet with a separator, a fan and sometimes a lid that closes the opening off neatly. Reckon on a broad range of roughly 400 to 1200 euros for the well known brands. As an indication, the Camper-Style guide quotes prices such as Trobolo at around 649 to 1145 euros, Kildwick at around 449 to 799 euros and Nature’s Head at around 1099 euros; Separett has models from about 120 euros for a simple portable toilet up to around 900 euros for a complete unit (Camper-Style, Separett). Prices vary, so treat this as a guideline, not a fixed price.
Upsides: nice finish, reliable fan, ready to use straight away. Downside: the price.
Building it yourself. A DIY toilet is essentially a wooden box with a separator, a bucket for the solids, a urine container and a toilet seat on a board. You buy a standalone separator as a separate part. For materials, reckon on roughly 50 to 150 euros, depending on whether you count the separator and a fan (Altijd Voorbereid).
Upsides: cheap, made to measure, easy to repair. Downside: you have to sort out tidy ventilation and finishing yourself.
The DIY build in short
- Work out the dimensions. Measure the bucket and urine container you are using, and size the box around them. A comfortable seat height is roughly that of a normal toilet.
- Cut the box. Plywood of around 12 to 18 mm is sturdy enough. Screw the side, back and front panels together (Pasar).
- Make the top panel. Cut an opening that the separator drops into exactly, so urine at the front and solids at the back are collected separately.
- Fit the container and bucket. The urine container (with hose) goes under the channel of the separator, and the bucket goes under the rear opening, either with a compostable bag or simply loose with cover material.
- Sort out ventilation. Drill a hole for a vent pipe to the outside and fit a small 12V fan on it if you like. A toilet seat on top finishes the job.
Common DIY mistake: putting the bucket box inside a sealed cabinet with no air outlet. Moisture then builds up and it starts to smell (Tiny House Life). So always arrange ventilation, DIY build included.
Installation: ventilation is half the job
With a composting toilet, ventilation is not an extra but the core of odour control. The fan or pipe continuously pulls a small amount of air out of the bowl to the outside. That does two things: it dries the solids (dry does not smell) and it draws any odour away before it reaches the room.
Pipe to the outside or up to the roof. Run the vent pipe outside, preferably upwards and above roof level, so the wind pulls the air away and no moisture sits in the duct. Keep the route as short and straight as you can.
Fan or no fan. With light use (a shed, occasional visits) a passive pipe with natural draught can be enough. With daily use in a tiny house or on a boat, a small electric fan is strongly recommended. The Separett fan uses very little: around 0.06 kWh per 24 hours, which runs happily off a battery or solar panel, and it suits a duct of up to about 6 metres with a maximum of three 90 degree bends (Separett Villa). So keep your duct as straight as possible.
Power. You connect a 12V fan to a battery or solar system, and a 230V model to the mains. An incinerating toilet, by contrast, needs a great deal of power or gas, so bear that in mind if you are off grid.
Positioning. Put the toilet on a level spot where you can easily reach the bucket and the container for emptying. Leave a bit of room around it, and never put it in a fully sealed cabinet without an air outlet.
Use: cover material, emptying and preventing smell
Which cover material do you use?
After every number two you cover the solids with dry, absorbent material. Suitable options are sawdust, wood fibre or wood shavings, coco coir, hemp fibre and ready made composting toilet litters (Ecosave/composttoilet). The key requirements: dry, highly absorbent and odour binding.
- Coco coir: sustainable, swells up with water, popular with brands like Nature’s Head.
- Wood fibre / sawdust: cheap and widely available, use untreated wood.
- Hemp fibre: light and very absorbent.
Better to use a bit too much cover material than too little: not covering enough is the most common cause of smell.
How often do you empty it?
That depends on the number of users and the container size. A practical rule of thumb: the urine container is the one you empty most often, frequently daily to a few times a week, because urine fills up fastest and starts to smell otherwise. The solids container lasts longer, from about a week with daily use by two people to several weeks with lighter use (Camper-Style). Empty the urine container in good time, because that is the single most important way to prevent odour.
Preventing smell: the short checklist
- Always keep urine and solids separated.
- Cover generously with dry material every single time.
- Empty the urine container well before it is full (it causes most of the smell).
- Make sure ventilation to the outside actually works.
- Close the opening after use (lid or slider) if your toilet has one.
Cleaning
Clean the urine container and the urine channel regularly, because that is where deposits and ammonia smell build up. Rinse the container out with water, and use a little cleaning vinegar against limescale and urine scale if needed. Rinse out the solids container after emptying and let it dry properly. Do not use harsh chemicals if you want to compost the contents.
What do you do with the contents?
This is the part people have the most questions about, and the part where you need to be careful. There is a clear difference between urine and solids, and between what seems handy and what is actually allowed.
Urine as fertiliser
Fresh urine is rich in nitrogen and in itself a decent fertiliser, but handle it carefully. A few points from reliable sources:
- You may use urine for your own purposes in your own garden, but under fertiliser legislation it cannot be traded as a fertiliser or applied in conventional agriculture (WUR, for the Netherlands).
- Dilute urine with water before giving it to plants; undiluted it is too concentrated and can burn them (Saniwijzer).
- For safe use, storing the urine so it matures before you spread it is advised.
Not sure what is allowed where you are, for example on an allotment or a holiday park? Check the rules with your local council or water authority. The Dutch site Saniwijzer sets out the framework around discharge and reuse.
Composting the solids
You compost the solids on a separate compost heap, not with your regular garden and kitchen waste. Human waste can contain pathogens, so the rule here is: longer composting time and plenty of caution.
- Use a separate, closed compost heap or compost bins, kept apart from your kitchen compost.
- Count on a long maturing time. Sources mention several months to a year for ordinary compost; for human compost, the specialist literature deliberately allows for a longer, safe maturing period (Velt). In short: give it plenty of time.
- Use the mature end product around ornamental plants or shrubs at most, not around edible crops, unless you are certain it has been processed safely.
Want to be sure whether you are allowed to make and use human compost on your plot? Ask your local council or water authority. The rules can differ per location and situation, and it is wise to check this beforehand rather than afterwards.
Common mistakes
- Bucket in a sealed cabinet with no ventilation. Moisture builds up and it starts to smell. Always arrange an air outlet.
- Too little cover material. The solids have to stay dry and covered, so be generous with it.
- Emptying the urine container too late. This is the number one cause of odour. Empty it more often than you think you need to.
- Undiluted urine on plants. Too concentrated, and it burns leaves. Always dilute.
- Throwing solids in with the regular garden waste. They belong on a separate compost heap with long maturing, not in the green bin.
- Choosing the wrong type for your use. A basic bucket toilet will not cope as a stopgap for a family using it heavily every day, so go for a model with a fan in that case.
Maintenance
A composting toilet is low maintenance, but not no maintenance. Keep the urine container and channel free of limescale and deposits, check that the fan is running and the duct is clear, and replace compostable bags on time. Let the containers dry after emptying before you put them back. With a 12V fan: keep an eye on the battery or solar panel, because if the fan stops, the smell comes back.
Who is a composting toilet right for (and who not)?
A good fit if you are off grid or without a sewer connection, want to save water (a dry toilet can save up to around 15,000 litres of drinking water per person per year according to several sources, Off-grid Centrum), or you are simply conscious about closing loops. Ideal for a shed, tiny house, boat, camper van and off-grid living.
Less of a fit if you do not fancy emptying it regularly, have no space for a compost heap, or if several people use it heavily without you choosing a model with good ventilation. Anyone who really does not want the emptying is better off looking at an incinerating toilet, although that costs considerably more and demands a lot of energy.
Frequently asked questions
Does a composting toilet really compost inside the toilet itself?
No. The toilet collects and keeps things dry, but real composting only happens later on a separate compost heap that you let mature for a long time. So the name is a bit confusing.
Does a composting toilet smell?
Used properly, hardly at all. Odour mainly comes from urine and solids mixing. By separating them, using cover material generously and keeping the ventilation working, it stays virtually odour free. According to Separett, separation reduces odour by up to around 80 percent (Separett).
Do I need power?
Not necessarily. A basic model works with a passive vent pipe. With daily use a small fan is recommended; it uses very little (around 0.06 kWh per 24 hours for Separett) and runs perfectly on solar.
How often do I have to empty it?
The urine container most often (frequently daily to a few times a week), the solids container less often (from about a week with daily use by two people to several weeks with light use). Container size and the number of users decide it.
Can I use the contents in my garden?
You may use urine diluted for your own purposes in your own garden, but not trade it or apply it in conventional agriculture (WUR, for the Netherlands). The solids you compost separately with long maturing. If in doubt, check the rules with your local council or water authority, and take a look at Saniwijzer.
What is the difference with a chemical toilet?
A chemical toilet mixes everything in one tank with a chemical fluid and flushes with water; you empty it at a disposal point. A composting toilet uses no water and no chemicals and separates urine and solids, so you can reuse the contents.
Are you building a shed, tiny house or off-grid spot that a composting toilet would fit into nicely? Start with a well thought out plan. At Fred you will find clear building plans and DIY projects you can get going with yourself, from a garden shed to a complete self-build home. Have a look around at fredsdiyplans.com and just build it yourself. Good luck and enjoy the build.