What You Need to Build a Basic Composting Toilet
A composting toilet is a self-contained unit that breaks down human waste using sawdust, wood chips, or coconut coir instead of water. You can build one from a five-gallon bucket, a wooden box, or a larger cabinet — the core is the same: a seat over a container, a layer of carbon material (sawdust), and a way to separate liquids from solids. Most homemade versions cost between $50 and $300 in materials, depending on size and finish.
The simplest design works for occasional use — a cabin, RV, or backup toilet during water shortages. More elaborate versions handle daily use for a household. Both follow the same principle: each time you use it, you add a handful of sawdust or similar material to cover waste and absorb moisture. Over weeks or months, the contents break down into compost-like material that can be emptied and managed safely.
Key Takeaways
- A five-gallon bucket toilet is the fastest build and costs under $50; a wooden box toilet takes a weekend and costs $100 to $200.
- Sawdust, wood chips, or coconut coir are the carbon materials that make composting toilets work — you add a handful after each use.
- Liquid separation (using a divider or separate container) keeps the compost from becoming too wet and speeds decomposition.
- Finished compost should sit for at least six months after the last use before you handle it, and should never be used on food crops without informed guidance.
The Five-Gallon Bucket Toilet: Fastest Option
The five-gallon bucket toilet is the easiest build and works for temporary or occasional use. You need a five-gallon food-grade bucket with a lid, a toilet seat (a standard round seat from a hardware store, or a DIY seat cut from plywood), sawdust or wood chips, and a larger container or second bucket to catch liquids if you want to separate them.
Cut a hole in the bucket lid large enough for the toilet seat to fit snugly over it — typically 6 to 8 inches in diameter. Sand the edges smooth. Attach the seat to the lid using bolts or heavy-duty adhesive. Place the bucket inside a larger container or cabinet if you want to hide it, or leave it freestanding. After each use, add a handful of sawdust to the bucket. When the bucket is three-quarters full, empty it into a compost bin or pile and replace it with a clean bucket.
This design works well for camping, RVs, or a backup toilet in a shed. It does not separate liquids, so the contents will be wetter and take longer to break down — typically three to six months before it is safe to handle. If you want faster decomposition, add a second bucket underneath with a divider between them to catch urine separately.
Building a Wooden Box Toilet for Daily Use
A wooden box toilet is more durable and comfortable than a bucket, and it looks more like a conventional toilet. It takes a weekend to build and costs $100 to $200 in materials. You need exterior plywood or cedar boards, wood screws, a toilet seat, a five-gallon bucket or larger container to sit inside the box, sawdust, and optional hardware for a hinged lid or removable front panel.
Build a box roughly 18 inches wide, 18 inches deep, and 16 inches tall — large enough to fit a five-gallon bucket inside with room on the sides. Cut a hole in the top for the toilet seat (6 to 8 inches) and attach the seat with bolts. Drill small ventilation holes near the top of the back panel. Attach a hinged lid to the top so you can access the bucket underneath, or build a removable front panel. Sand all edges and explore exterior wood stain or sealant to protect against moisture.
Place a five-gallon bucket or larger container inside the box to catch waste. Add sawdust after each use. When the bucket is full, remove it, empty it into a compost pile, and replace it with a clean one. A wooden box toilet can handle daily use for one or two people and will last several years if you maintain the wood finish.
Separating Liquids to Speed Decomposition
Urine makes up about 90 percent of the liquid in human waste and slows down the composting process if left mixed with solids. Separating liquids cuts decomposition time roughly in half — from six months to three months — and makes the finished compost drier and easier to handle.
The simplest separator is a urine diverter: a curved insert that sits under the toilet seat and directs urine into a separate container while solids fall into the main bucket below. You can buy a commercial urine diverter for $30 to $80, or build one from PVC pipe and a funnel. The urine flows down a tube into a separate five-gallon bucket or larger container. Separate urine can be diluted with water (1 part urine to 8 parts water) and used as a nitrogen-rich fertilizer for ornamental plants and trees — never on food crops without informed guidance.
If you do not use a diverter, add extra sawdust — roughly twice as much as you would with separation — to keep the contents from becoming waterlogged. The compost will still work, but it will take longer and may smell stronger during decomposition.
Choosing and Using Carbon Materials
The carbon material you add after each use is what makes a composting toilet work. It absorbs moisture, reduces odor, and provides the carbon that microbes need to break down waste. The most common choices are sawdust, wood chips, and coconut coir.
Sawdust is the cheapest option — often free from woodworking shops or lumber mills — and works well in most climates. Use untreated sawdust only; treated wood contains chemicals that can harm soil. Wood chips are coarser and take longer to break down but last longer in the toilet before needing replacement. Coconut coir (the fiber from coconut husks) is more expensive but absorbs moisture very well and breaks down completely. Some people mix sawdust with leaves or grass clippings for variety.
Add a handful (roughly one-quarter cup) after each use. If the toilet starts to smell, add more sawdust — odor usually means the contents are too wet or not covered well enough. Store your carbon material in a dry place in a bucket or bin next to the toilet so it is always within reach.
Managing and Using Finished Compost
When your toilet bucket is full or you want to empty it, transfer the contents to an outdoor compost bin or pile. Finished compost should sit for at least six months after the last waste is added before you handle it or use it. This waiting period allows pathogens to die off and the material to fully stabilize.
Finished compost from a composting toilet should never be used on food crops — vegetables, fruits, or herbs — without informed testing and guidance. It can be used safely on ornamental plants, trees, shrubs, and lawns. Spread it as a soil amendment at a depth of one to two inches and work it into the top few inches of soil. If you are uncomfortable using it, you can bury it in a designated area of your property or dispose of it in a yard waste bin if your local program accepts it.
Keep records of when you emptied each bucket so you know which piles have aged long enough. Label your compost piles clearly if you have multiple ones at different stages. Store finished compost in a covered bin to keep it dry and prevent it from blowing away.
Ventilation and Odor Control
A composting toilet produces less odor than a conventional toilet if it is built and used correctly, but ventilation helps. Drill or cut small holes near the top of the back panel of a wooden box toilet — roughly one-quarter inch in diameter, spaced a few inches apart. These holes allow air to flow through the compost and help it break down faster.
If odor becomes a problem, the most common cause is too much moisture or not enough sawdust. Add more sawdust and let the toilet sit for a day or two without use if possible. If you have a urine diverter, make sure it is working correctly and urine is not mixing with solids. In very humid climates, you may need to add sawdust more frequently or use a desiccant material like coconut coir instead of regular sawdust.
Some people add a small battery-powered fan to the ventilation holes to improve air flow, but this is optional. A well-maintained toilet with good sawdust coverage should not smell noticeably worse than a conventional toilet.
Frequently Asked Questions
Can I use a composting toilet indoors year-round?
Yes, but you need good ventilation and regular maintenance. In cold climates, decomposition slows dramatically in winter, so the compost may sit for months without breaking down. Keep the toilet in a heated space if possible, and be prepared to empty it less frequently but store full buckets until spring when decomposition can resume.
What happens if I run out of sawdust?
The toilet will still work but will smell and become wetter. Dried leaves, shredded paper, or even soil can substitute in a pinch, though they are less effective than sawdust. Keep a backup supply on hand. If you are caught without any carbon material, use the toilet as little as possible until you can get more sawdust.
Is it legal to have a composting toilet?
Laws vary by location. Some areas allow composting toilets as primary toilets; others allow them only as backup or secondary toilets. Check your local building codes and health department rules before you build. In many places, you need a permit or inspection. Contact your county health department or building inspector to learn what is allowed in your area.
How long does it take for waste to fully compost?
With liquid separation and good sawdust coverage, finished compost is ready to handle in three to four months. Without separation, it takes six months to a year. After you remove it from the toilet, it should sit for at least another six months before you use it on plants. Total time from use to safe process is typically nine months to a year.
Can I use finished compost in a vegetable garden?
No. Finished compost from a composting toilet should not be used on food crops. It can be used on ornamental plants, lawns, and trees. If you want to use it on vegetables, you would need laboratory testing and informed guidance on safe process rates, which most homeowners do not pursue. Treat it as a soil amendment for non-food plants only.