A composting toilet is a waterless toilet that breaks down human waste into compost using sawdust, peat moss, or coconut coir instead of flushing it away

The basic idea is straightforward: after you use the toilet, you add a layer of dry material (usually sawdust) on top of the waste. Over time, microbes and fungi break everything down into a dark, soil-like substance you can use in gardens or landscaping. No plumbing, no septic tank, no water bill. You build one from a 5-gallon bucket, a toilet seat, a container for the dry material, and a way to ventilate odors.

A composting toilet works best in cabins, RVs, off-grid homes, or anywhere septic systems are impractical or expensive. It also works in regular homes as a backup or supplement. The catch: you have to empty and manage it yourself, and it requires discipline about adding the dry material every single time. If you skip that step, you get smell and flies.

Key Takeaways

  • A basic composting toilet uses a 5-gallon bucket, a toilet seat, sawdust or similar dry material, and a vent pipe to control odor.
  • You must add dry material after every use—this is not optional if you want to avoid smell and pest problems.
  • The finished compost takes 6 to 12 months to fully break down and should only be used on ornamental plants or trees, not on food crops.
  • A composting toilet costs $50 to $300 to build yourself, depending on materials and whether you add a urine diverter.
  • Ventilation is the single most important factor in preventing odor; a vent pipe running outside is essential, not optional.

What You Need to Build a Basic Composting Toilet

Start with a 5-gallon food-grade bucket with a lid—the kind restaurants get cooking oil or pickles in. You can buy new ones from hardware stores for $5 to $10, or ask a bakery or restaurant for used ones free. Drill a hole in the lid large enough for a standard toilet seat to bolt through, or buy a toilet seat designed for 5-gallon buckets (around $20 to $40 online).

You will also need a vent pipe—typically 3-inch or 4-inch PVC pipe that runs from the bucket to outside, at least 6 feet above ground level. This is what stops the smell. Add a vent cap (a mushroom-shaped hood) at the top to keep rain out. The pipe, cap, and fittings cost $30 to $60.

For the dry material, buy sawdust (untreated wood only—no pressure-treated lumber), peat moss, or coconut coir. Sawdust is cheapest and works well; you can get it free from woodworking shops or buy bags at garden centers for $5 to $15. Keep it in a bucket next to the toilet with a small scoop inside.

Optional but useful: a urine diverter (a funnel insert that separates liquid from solids) speeds decomposition and reduces odor. These cost $30 to $100 and require a separate container for urine, which you can dilute and use as fertilizer.

Step-by-Step Assembly

Start by preparing the bucket. If you are using a standard 5-gallon bucket with a lid, drill a hole in the center of the lid about 10 to 12 inches in diameter—large enough for the toilet seat to fit snugly. Sand the edges smooth so they do not cut anyone. Bolt the toilet seat to the lid using stainless steel bolts and washers so it does not rust.

Drill a smaller hole (about 3 to 4 inches) in the side of the bucket near the bottom. This is where the vent pipe connects. Use a rubber coupling or PVC fitting to attach the vent pipe securely. The pipe should run straight up and outside, sloping slightly upward so condensation does not drip back into the bucket. At the top, attach the vent cap.

Place the bucket inside a wooden box or cabinet if you want it to look like a regular toilet. The box can be straightforward—just four sides and a front panel with a hole cut for the seat. Make sure air can flow underneath and around the bucket so the vent pipe works properly. Leave the back or one side open for straightforward bucket removal.

Fill a separate container (a 5-gallon bucket works) with your dry material and place it next to the toilet with a small scoop. A coffee can or soup ladle works fine as a scoop. Label it clearly so no one mistakes it for something else.

How to Use and Maintain Your Composting Toilet

After each use, add a scoop of dry material—about 2 to 3 inches—on top of the waste. This is the most important step. The dry material absorbs moisture, covers odors, and provides carbon for the microbes that break down the waste. If you skip this step even once, you will smell it.

Keep the toilet seat and lid closed between uses so odors do not escape into the room. The vent pipe should handle all the smell if it is installed correctly. If you notice odor inside the room, check that the vent pipe is not blocked and that the seal between the bucket and the lid is tight.

When the bucket is about three-quarters full, it is time to empty it. Wear gloves and a dust mask. Dump the contents into a compost bin, a large container, or a designated pile in your yard. Rinse the bucket with a hose, dry it, and put it back. Do not use the same bucket continuously without cleaning it—have two buckets and rotate them so one can rest while the other is in use.

The material in your compost pile will continue to break down over 6 to 12 months. Turn it occasionally with a pitchfork or shovel to speed decomposition. When it is dark, crumbly, and smells like soil, it is ready to use. Only explore it to ornamental plants, trees, shrubs, or landscaping—never on vegetables, herbs, or food crops, because human waste can carry pathogens that cooking does not always kill.

Ventilation: Why It Matters and How to Get It Right

The vent pipe is the difference between a composting toilet that works and one that smells like a portable outhouse. Air naturally rises, so warm air and odors from the bucket want to escape upward through the pipe. If the pipe is blocked, too short, or poorly sealed, those odors come back into the room instead.

The pipe should be at least 6 feet tall and extend above the roofline or highest point of your building. It should slope slightly upward from the bucket to the exit so gravity helps move air up and out. Use rigid PVC pipe, not flexible dryer vent hose, because flexible hose can sag and trap condensation.

Seal all connections with PVC cement or stainless steel hose clamps so air does not leak out the sides. At the top, install a vent cap that keeps rain and insects out but lets air escape. Some people add a solar vent fan to the pipe to pull air out faster, which helps in cold climates or very humid conditions. A small solar fan costs $30 to $80 and runs on sunlight with no electricity bill.

In winter, condensation can form inside the pipe and drip back into the bucket. Insulating the pipe with foam pipe wrap helps prevent this. If you live somewhere very cold, you may need to run a small heat tape inside the pipe to keep it warm enough that condensation does not form.

Urine Diverters: Separating Solids and Liquids

A urine diverter is a funnel-shaped insert that sits inside the toilet seat. It directs urine into a separate container while solids fall into the main bucket below. This has two big advantages: urine is mostly sterile and does not need to compost, so you can use it right away as a fertilizer (diluted 10 parts water to 1 part urine). And removing liquid from the solids means they dry out faster and smell less.

Diverters come in two types: front-facing (for people with a penis) and dual-use (designed to work for all users, though they require more careful aim). Dual-use models are more expensive but more practical for shared bathrooms. Popular brands include Nature's Head and Separett, though simpler DIY versions exist.

If you add a diverter, you will need a second container—usually a 5-gallon bucket or a larger carboy—to collect urine. Empty it every few days into a garden or dilute it in a watering can. The urine bucket needs a lid to prevent smell and spills. This adds complexity, so start with a basic composting toilet first and add a diverter later if you want to.

Common Problems and How to Fix Them

Smell inside the room: Check that the vent pipe is not blocked (leaves, nests, or ice can clog it). Make sure the lid seals tightly to the bucket and the toilet seat. Verify that the vent pipe is tall enough and slopes upward. If the pipe is correct, you may not be adding enough dry material—increase the amount you add after each use.

Flies or gnats: These come from moisture and decomposing material. Add more dry material to absorb moisture. Make sure the vent cap keeps insects out. If flies are already in the bucket, empty it sooner and clean it thoroughly. Store dry material in a sealed container so flies do not breed in it.

Wet, mushy material that does not decompose: You are not adding enough dry material, or the bucket is too wet. Increase the amount of sawdust or peat moss you add. If the bucket is sitting on damp ground, raise it on blocks so air can flow underneath. In very humid climates, you may need to empty the bucket more often.

Frozen pipes in winter: If the vent pipe freezes, air cannot escape and odors back up into the room. Insulate the pipe with foam wrap and consider adding a solar vent fan or heat tape to keep it warm.

Cost Breakdown and Timeline

A basic composting toilet costs $50 to $150 to build. A 5-gallon bucket is $5 to $10, a toilet seat is $20 to $40, PVC pipe and fittings are $30 to $60, and dry material is free to $15. If you add a urine diverter, add another $30 to $100. If you build a wooden cabinet around it, add $50 to $200 depending on materials and whether you do the work yourself.

The timeline from start to finished compost is long. After you empty the bucket, the material takes 6 to 12 months to fully break down into usable compost. This means you need space for a compost pile or bin, and you need to be patient. If you have multiple people using the toilet, you will fill buckets faster and need to empty them more often—plan for weekly or twice-weekly emptying in a household of four.

Frequently Asked Questions

Can I use a composting toilet in a regular house with plumbing?

Yes. Some people use a composting toilet as a backup or in a guest bathroom to save water. You can keep your regular toilet and add a composting toilet elsewhere. The main limitation is space—you need room for the toilet, a compost pile, and dry material storage. It works best if you have land outside.

What if I do not have space for a compost pile?

You can store full buckets in a shed or garage until you have enough material to compost, or you can take the material to a community garden or landscaper who accepts compost. Some people bury the material directly in a garden bed under trees or shrubs. Do not throw it in the trash—it is still human waste and needs to decompose properly.

Is composting toilet waste safe to use on a vegetable garden?

No. Human waste can carry pathogens that survive composting unless the pile reaches very high temperatures (above 140°F for weeks), which is hard to achieve at home. Use finished compost only on ornamental plants, trees, shrubs, and landscaping. If you want to use it on food crops, research advanced composting methods or consult a local agricultural extension office.

Do I need a permit to build a composting toilet?

It depends on your location and whether you are replacing a septic system or adding one as a supplement. Some counties require a permit; others do not. Check with your local health department or building inspector before you build. If you are in an RV or cabin on private land, you usually have more freedom than in a residential neighborhood with codes.

How often do I need to empty the bucket?

This depends on how many people use it and how much dry material you add. One person using it daily might empty it every 2 to 4 weeks. A household of four might empty it weekly. Start by emptying it when it is about three-quarters full and adjust based on how fast it fills. Keep a second bucket ready so you always have one in use.