The basic operation: what happens each time you use it

A compost toilet works by separating liquid waste from solid waste, then breaking down the solid waste with sawdust, leaves, or coconut coir instead of water. When you use it, you sit or stand as you would on a regular toilet. After you finish, you add a handful of the dry material (usually kept in a bucket beside the toilet) to cover what you just deposited. The liquid drains into a separate tank or container below, and the solid waste stays in the main chamber where it begins to decompose.

The dry cover material is essential — it absorbs moisture, controls odor, and speeds decomposition by introducing carbon. Without it, the toilet becomes wet, smelly, and slow to break down waste. Most compost toilets come with a small scoop or cup attached to the seat or mounted on the wall nearby. Use it every single time.

Some models have a foot pedal or handle that shifts the waste into a separate chamber after each use. Others rely on gravity and the dry material to keep things separated. Read your toilet's manual to see which type you have, because the steps differ slightly.

Key Takeaways

  • Add a handful of dry cover material (sawdust, leaves, or coconut coir) after every use to control odor and speed decomposition.
  • Empty the liquid tank regularly — weekly or monthly depending on household size — to prevent overflow and reduce smell.
  • The solid waste chamber needs emptying every few months to a year, depending on how many people use the toilet and the chamber size.
  • Finished compost (dark, crumbly, odorless material) can take six months to two years to fully cure and is safe to use on ornamental plants and trees.
  • Never put toilet paper, feminine hygiene products, or anything other than human waste and cover material into the toilet.

Emptying the liquid tank

The liquid tank sits below the toilet and collects urine and any liquid that drains from the solid waste. Check it weekly at first to see how fast it fills — this depends on how many people use the toilet and how much liquid they consume. In a household of two, the tank might fill every two to four weeks. A family of four could fill it every week.

When the tank is full or nearly full, remove it (most slide out or unhook from the side) and empty it into a toilet, drain, or outdoor area away from wells and water sources. Rinse the tank with a hose if it smells, then replace it. Some people dilute the liquid with water and use it as fertilizer for trees and shrubs, but never on vegetables or herbs you eat raw. If you choose to do this, dilute it at least 10 parts water to 1 part liquid.

If your toilet has a drain line running to a separate tank outside, you may not need to empty anything manually — the tank handles it. Check your manual to see whether your model has this feature.

Emptying and managing the solid waste chamber

The solid waste chamber is where the actual composting happens. Depending on your toilet's design, it might be a removable bucket, a sealed chamber below the seat, or a larger tank that you access from outside. Check your manual to find out how to access it on your model.

Empty the chamber when it reaches the fill line or when you notice it is getting full — usually every three to six months for a household of two, or every one to two months for a larger family. Some toilets have a second chamber that you switch to while the first one sits and decomposes, which is more convenient than emptying frequently.

When you empty it, transfer the contents into a compost bin, pile, or designated area in your yard. Spread it in layers with other compost materials (leaves, grass clippings, food scraps) if you have them, or let it sit in a covered pile on its own. The material will continue to break down over the next six months to two years. Once it is dark, crumbly, and smells like soil, it is finished compost and safe to use around trees, shrubs, and ornamental plants.

Never use uncomposted or partially composted human waste on vegetables, herbs, or any food crops. Wait until it is fully finished and dark before explore it anywhere near food.

Choosing and using cover material

Sawdust is the most common cover material and works well if you have access to it from a woodworking shop, lumber yard, or hardware store. Use untreated sawdust only — treated wood contains chemicals that slow decomposition. A five-gallon bucket of sawdust lasts a household of two about two to four weeks.

Coconut coir (shredded coconut husk) is a commercial alternative sold in compressed bricks at garden centers and online. It absorbs moisture well and breaks down completely. One brick makes several buckets of material and costs between five and fifteen dollars.

Dried leaves, straw, or shredded paper also work, though they are less absorbent than sawdust or coir. If you use leaves or straw, chop them finely so they pack down and cover waste completely. Shredded paper (newspaper, cardboard, office paper) works in a pinch but can clump when wet.

Keep your cover material in a bucket with a lid next to the toilet. Scoop a handful after each use — roughly the volume of a tennis ball. If the toilet starts to smell, you are not using enough cover material. Add more with each use until the odor stops.

Troubleshooting common problems

Odor: This almost always means you are not adding enough cover material or you are not emptying the liquid tank often enough. Add more material with each use and empty the liquid tank more frequently. If the smell is coming from the solid waste chamber, the material inside may be too wet — mix in more dry material when you empty it next time.

Liquid leaking or overflowing: The liquid tank is full. Empty it when ready. If it fills faster than expected, someone in the household is using much more liquid than average, or there is a leak in the toilet itself. Check all connections and seals, and consider emptying the tank more often.

Slow decomposition or wet, sludgy material: The solid waste is not getting enough carbon (dry material). Add more cover material with each use, and when you empty the chamber, mix the contents with additional sawdust or coir before putting it in your compost pile. Decomposition speeds up when the material is drier.

Insects or fruit flies: These are attracted to moisture and exposed waste. Make sure you are covering waste completely with dry material every time, and keep the cover material bucket sealed. If flies are already present, sprinkle a thin layer of diatomaceous earth (food-grade) over the waste when you empty the chamber.

What you can and cannot put in a compost toilet

Safe to put in: Human urine and feces only. That is it. Everything else either slows decomposition, introduces pathogens, or creates odor and pest problems.

Never put in: Toilet paper (use a separate trash bin for it, or use a bidet and skip paper entirely), feminine hygiene products, diapers, pet waste, food scraps, grease, medications, cleaning chemicals, or anything else. Even "flushable" wipes do not belong — they do not break down in a compost toilet and will clog or jam the system.

If someone in your household cannot follow this rule, a compost toilet is not practical for your situation. Consider a conventional septic system or municipal sewer instead.

Maintenance and seasonal care

Check the toilet monthly for leaks, cracks, or loose connections. Wipe down the seat and lid with a damp cloth — no harsh chemicals needed. If you use a wooden seat, sand and oil it once a year to prevent rot.

In winter, if your toilet is in an unheated space, decomposition slows dramatically. You may need to empty the solid waste chamber less often, but you should still empty the liquid tank regularly because it can freeze. If you live in a very cold climate, consider insulating the toilet or moving it to a heated space during winter months.

If you are leaving the toilet unused for more than a few weeks, empty both tanks completely before you go. When you return, add fresh cover material and let the system restart.

Frequently Asked Questions

Can I use a compost toilet in an apartment or rental?

Most apartments and rentals do not allow compost toilets because they require space for a compost pile and may violate local plumbing codes. Check your lease and local regulations before installing one. Portable compost toilet seats that sit on top of a regular toilet are sometimes permitted, but confirm with your landlord first.

How long until the compost is ready to use?

Finished compost typically takes six months to two years, depending on temperature, moisture, and how often you mix the pile. Warmer climates and active mixing speed it up. The material is ready when it is dark brown or black, crumbly, and smells like soil with no odor of waste.

What if I have guests — do I need to explain how to use it?

Yes. Show them the cover material bucket and explain that they need to add a handful after use. Most people understand quickly once they see it. Keep the instructions posted on the wall or inside the toilet lid as a backup.

Is the finished compost safe for vegetable gardens?

No. Use finished compost only on ornamental plants, trees, and shrubs. Human waste compost is not recommended for food crops because of potential pathogen survival, even after composting. If you want to use it on food plants, research local regulations and best practices for your region first.

What happens if the toilet freezes in winter?

The liquid tank can freeze and crack. If you live in a cold climate, drain both tanks before winter or insulate the toilet with blankets and heat tape. Some people move their compost toilet indoors during the coldest months or switch to a conventional toilet temporarily.