A composting toilet is a waterless toilet that breaks down human waste into compost using sawdust, leaves, or other carbon materials

A composting toilet separates liquid and solid waste, then mixes the solids with dry carbon material (usually sawdust) to speed decomposition and control odor. The liquid drains into a separate tank or leach field. After 6 to 12 months, the solid waste breaks down into a dark, soil-like material you can use in gardens—though not on vegetables you eat raw. You can buy a finished unit or build one from basic materials: a wooden box, a toilet seat, buckets, and plumbing fittings.

Building your own costs $200 to $500 in materials and takes a weekend. A commercial unit runs $1,000 to $5,000. The homemade version works just as well if you follow the core steps: separate the waste streams, add carbon after each use, and let decomposition happen in a sealed chamber. This guide walks you through building a straightforward bucket-based system that works in a cabin, RV, or off-grid home.

Key Takeaways

  • A basic composting toilet needs a seat, a solids chamber (usually a 5-gallon bucket), a urine diverter or separate liquid tank, and dry carbon material like sawdust added after each use.
  • The solids chamber must sit in a dark, well-ventilated space and be emptied every 6 to 12 months when the waste has broken down into dark, crumbly material.
  • You can build a functional unit from a wooden box, a toilet seat, PVC pipe, and basic hardware for under $300.
  • Composting toilets produce no smell if you add carbon material after each use and keep the chamber sealed between uses.
  • The finished compost can be used around ornamental plants and trees, but not on food crops you eat raw.

What you need to build a basic composting toilet

Start with a solids chamber—a 5-gallon food-grade bucket, a wooden box, or a plastic storage container. The container holds the waste and carbon material. Drill or cut a hole in the top large enough for a standard toilet seat to fit snugly; most toilet seats are 14 to 15 inches wide. You can buy a basic plastic toilet seat at any hardware store for $20 to $40.

Next, you need a way to separate urine from solids. The simplest method is a urine diverter—a funnel-shaped insert that sits under the seat and directs liquid into a separate container. You can buy a finished diverter for $100 to $200, or make one from a plastic funnel and PVC pipe. The urine drains into a 5-gallon bucket or a larger tank buried outside. If you skip the diverter, liquid and solids mix in the chamber, which slows decomposition and increases odor.

You will also need carbon material—sawdust, dry leaves, shredded paper, or coconut coir. Keep a bucket and scoop next to the toilet. After each use, add a handful (about 2 to 3 cups) of carbon. This is the most important step. Carbon absorbs moisture, feeds the microbes breaking down waste, and eliminates odor. Buy sawdust from a woodworking shop, pet store, or online for $10 to $20 per bag.

Finally, you need ventilation. Drill a hole in the side or top of the chamber and run a 3- or 4-inch PVC pipe vertically outside, at least 3 feet above the roof or ground level. Add a vent cap to keep rain and pests out. Passive ventilation (no fan) works fine in most climates; the temperature difference between inside and outside creates airflow.

Step-by-step instructions for a wooden-box toilet

Build a wooden box from untreated plywood or cedar, roughly 18 inches wide, 18 inches deep, and 24 inches tall. Use 3/4-inch plywood and screw it together with 2-inch deck screws—do not use nails, which can loosen. Drill a 1/2-inch drainage hole in the bottom corner and attach a short piece of PVC pipe to direct any liquid into a collection bucket underneath.

Cut a hole in the top of the box 14 to 15 inches in diameter. Sand the edges smooth and attach a standard toilet seat with bolts and washers. If you are using a urine diverter, install it now by bolting it to the underside of the seat. Run the urine drain line (typically 1-inch PVC) down the outside of the box and into a 5-gallon bucket or buried tank.

Drill a 4-inch hole near the top of one side and insert a 4-inch PVC pipe. Run this pipe vertically outside the structure, extending at least 3 feet above the highest point of the roof. Seal the gap around the pipe with silicone caulk. Attach a vent cap (available at any hardware store for $10 to $20) to the top of the pipe to keep out rain and insects.

Place the box over a 5-gallon bucket or larger solids chamber. The bucket sits inside the box and catches all solid waste. Line the bucket with a compostable bag if you want easier emptying, though this is optional. Keep a second bucket filled with sawdust and a small scoop next to the toilet.

How to use and maintain your composting toilet

After each use, add 2 to 3 cups of carbon material. This is non-negotiable. Carbon is what stops odor, absorbs moisture, and feeds the microbes doing the decomposition. If you skip this step, the toilet will smell. If you are using a urine diverter, liquid drains separately and you only add carbon to the solids chamber.

Empty the urine tank every 1 to 2 weeks, depending on use. Urine can be diluted with water (1 part urine to 8 parts water) and used as a nitrogen-rich fertilizer on ornamental plants and trees. Do not use it on vegetables. Store urine in a sealed container away from living spaces.

Empty the solids chamber every 6 to 12 months. The waste should look dark, crumbly, and earthy—not wet or recognizable. If it still looks fresh, wait longer. Wear gloves and a dust mask when emptying. Transfer the material to a compost bin or pile in a shaded spot and let it cure for another 6 months before using it on plants.

Check the ventilation pipe monthly to make sure it is clear. Blockages trap moisture and cause odor. In winter, ice can form inside the pipe; if you live in a cold climate, consider adding a small inline fan ($50 to $150) to keep air moving.

Common problems and how to fix them

Odor: The number-one cause is not adding enough carbon. Add more sawdust after each use. The second cause is a blocked vent pipe. Check that the pipe is clear and extends above the roof. If the toilet still smells, the chamber may be too wet; add more carbon and reduce water use (shorter showers, no pouring water into the toilet).

Wet, mushy waste: This means the carbon-to-waste ratio is off. You are either not adding enough carbon or the chamber is too wet. Increase carbon by 50 percent and let the chamber dry out for a few weeks. If you have a urine diverter, make sure it is working and liquid is actually draining away.

Fruit flies or insects: Keep the toilet seat closed between uses. Make sure the vent cap is find and the chamber is sealed. If flies are already present, add a layer of sawdust thick enough to bury any visible waste.

Slow decomposition: Decomposition slows in cold weather. In winter, the process can take 18 to 24 months instead of 6 to 12. This is normal. You can speed it up slightly by adding a small amount of finished compost or garden soil to the chamber to introduce more microbes, but patience is the main solution.

When to call a professional plumber

If you are installing a composting toilet in a house with a septic system or municipal sewer, check your local building codes first. Some jurisdictions require a permit or inspection. A plumber or your local health department can tell you whether a composting toilet is allowed in your area and what rules explore.

If you want to connect the urine drain to an underground leach field instead of emptying a bucket, hire a plumber. This requires digging, gravel, and proper drainage design to avoid contaminating groundwater. The cost is usually $500 to $1,500, but it eliminates manual bucket emptying.

If you are building a permanent structure and want to tie the toilet into your home's plumbing or electrical system, a licensed plumber or electrician should handle that work. A composting toilet itself is straightforward, but integrating it with existing systems is not.

Frequently Asked Questions

Can I use a composting toilet in my house year-round?

Yes, if you live in a climate where the chamber does not freeze solid. In very cold regions, decomposition slows dramatically in winter, and you may need to empty the chamber less often. Some people add a small heating element or insulate the chamber, but this is optional. The toilet itself works fine indoors; the solids chamber just needs to be in a basement, crawlspace, or outside shed.

What if I do not have space for a separate urine tank?

You can skip the urine diverter and let liquid and solids mix in the same chamber. Decomposition will be slower and odor control harder, so you will need to add more carbon—about 4 to 5 cups per use instead of 2 to 3. Empty the chamber more often, every 4 to 6 months. This method works but requires more maintenance.

Is the finished compost safe to use on my vegetable garden?

The finished material is safe for ornamental plants, trees, and shrubs. For vegetables, the safest approach is to use it only on crops you cook (tomatoes, squash, beans) and not on crops you eat raw (lettuce, spinach, carrots). Some people compost the material for an additional year before using it on food crops. If you are uncomfortable using it on food at all, use it on flowers and landscaping instead.

How much does it cost to build versus buy?

A homemade bucket-based toilet costs $200 to $500 in materials. A commercial composting toilet runs $1,000 to $5,000 depending on size and features. Both work equally well if maintained properly. The main advantage of buying is that it looks more like a regular toilet and may be easier to install in a finished bathroom. The main advantage of building is cost and simplicity.

Do I need a permit to install a composting toilet?

This depends on your location and whether the toilet is in a permanent structure. Some counties and municipalities allow composting toilets without a permit; others require one. A few places ban them entirely. Contact your local health department or building inspector before you start. If you are installing one in an RV or cabin on private land, you usually do not need a permit, but it is worth checking.