Composting Toilets: The Complete Guide (How They Work, Build vs Buy & Is It Legal?)

Everything you need to choose, build or install a composting toilet, with a free cost comparison.

A composting (or dry) toilet uses no water and no sewer connection. That makes it popular for off-grid cabins, tiny homes, vans, boats and places where a septic system is costly or impossible. This guide explains how they work, how to choose or build one, and what the law usually requires. The calculator compares DIY and buying.

Compare top composting toilets → COMPOCLOSET_AFFILIATE

Illustration: a composting toilet for an off-grid cabin.

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Planning estimates only. Bin capacity varies a lot by model and by how many uses are urine-only.

1. How composting toilets work

Instead of flushing waste away with water, a composting toilet holds it with a carbon "cover material" such as coconut coir, peat moss or sawdust, keeps it relatively dry and aerated, and vents odors outside. Aerobic decomposition then reduces the waste to roughly 10-30% of its original volume. The US EPA notes that temperatures in composting toilets typically don't get high enough to kill pathogens quickly, so time and good conditions (moisture around 40-70%, airflow) matter most, and that the resulting humus must be buried or removed by a licensed septage hauler in line with state and local rules. The standard for certified units is NSF/ANSI 41 (Non-Liquid Saturated Treatment Systems).

2. The main types

Type	How it works	Best for
Self-contained, urine-diverting	Separates urine at the bowl; solids drop into a bin you empty	Vans, tiny homes, cabins
Self-contained, mixing (with agitator)	Everything in one chamber, mixed with a crank and heated or vented	Cabins, light full-time use
Central / remote (large)	Toilet upstairs, big composting tank below	Full-time homes, high use
DIY bucket ("loveable loo"-style)	5-gallon bucket plus cover material, emptied to an outdoor compost pile	Budget, emergencies, occasional use

3. Why urine diversion matters

Diagram: parts of a urine-diverting dry toilet.

Most of the smell in a "dry" toilet comes from urine and feces mixing into a wet, anaerobic mass. Diverting urine keeps the solids chamber drier and far less smelly, and it lets the solids bin last much longer. Urine is collected in a bottle (emptied often) or sent to an approved drain or soil system where rules allow it.

4. Build vs buy

DIY: a bucket toilet built into a wooden box with a seat, plus a urine diverter insert, can be put together for well under $200. It works well if you keep it covered and empty it often, but it isn't certified and may not satisfy a permit. Buy: commercial units generally cost from several hundred to a couple of thousand dollars. You get sealed bins, a vent fan, better odor control and, on some models, NSF/ANSI 41 certification.

Popular commercial options (costs change, so check current listings):
CompoCloset COMPOCLOSET_AFFILIATE
Trelino TRELINO_AFFILIATE
Separett SEPARETT_AFFILIATE

Going DIY? See a urine-diverter DIY kit ETSY_TOILET_KIT

5. Venting

A small, continuously running fan drawing air from the solids chamber out through a vent pipe or wall vent keeps the room odor-free. Run the vent as straight as possible, terminate it outdoors above the roofline or away from windows, and add an insect screen. Most units use a low-wattage 12 V fan, which suits solar setups.

6. Emptying and what to do with the compost

Diagram: the solids cycle.

Urine: empty often (every 1-3 days in full-time use). Diluted urine is used as fertilizer in some places; check local rules.
Solids: follow your state/county rules first. EPA guidance says the end product must be buried or removed by a licensed septage hauler per state and local regulations. Where home composting is allowed, use a dedicated, covered outdoor bin well away from wells, streams, other water sources and food gardens, and let it cure undisturbed for about a year after the last addition. Low-temperature home compost is not proven pathogen-free: don't use it on edible crops (especially root crops or anything eaten raw) unless your local rules explicitly allow it; ornamentals and trees only.
Wear gloves (and ideally eye protection) when emptying, keep a dedicated set of tools, and wash your hands with soap and water afterward. Keep children and pets away from bins.
Ventilation: keep the vent fan running and the vent sealed and routed outdoors, per the manufacturer's instructions, to control odor, moisture and flies.
Where composting isn't allowed, some jurisdictions allow bagged solids to go to municipal trash. Check first.

7. Is a composting toilet legal?

In the US, on-site wastewater is regulated by states and county health departments, so the answer depends on where you live. Common patterns:

Some states explicitly allow composting toilets, sometimes only if they're NSF/ANSI 41 certified.
Many still require a greywater or septic system for sinks and showers, even with a composting toilet.
Homes needing a certificate of occupancy may be required to have a conventional, code-approved toilet as well.
RVs, vans and boats have their own rules, so check campground and marina policies.

Call your county or local health department / on-site wastewater office (and check HOA rules) before you buy or build, and get any required permit in writing.

8. Composting toilets off-grid

For cabins without water or septic, a composting toilet removes the biggest infrastructure cost. Pair it with a simple greywater plan for sinks and a solar panel for the fan. Freezing temperatures slow composting a lot, so seasonal cabins mostly store waste through winter and compost it in warm months.

9. Mistakes to avoid

Letting the solids get wet (it'll smell, so divert urine and add enough cover)
No fan or a leaky vent
Putting raw contents on vegetable beds
Buying before checking permit requirements
Underestimating how often a bin fills in full-time use

Compare composting toilets → COMPOCLOSET_AFFILIATE

Frequently asked questions

Do composting toilets smell?

A well-set-up urine-diverting toilet with a vent fan and enough cover material should have little to no odor. Smell usually means it's too wet or the vent isn't working.

Are composting toilets legal in the US?

It depends on your state and county. Some allow them (often requiring NSF/ANSI 41 certification), and many still require a greywater or septic system. Check with your county health department.

How often do you empty a composting toilet?

Urine bottles every day or few days in full-time use. Solids bins range from about weekly to monthly depending on the model and how many people use it.

Can I use the compost on my vegetable garden?

It's generally advised not to use it on edible crops unless your local rules allow it and the material has been properly composted. Use it on ornamental plants.

Can I build my own composting toilet?

Yes. A bucket toilet with cover material, or a box build with a urine diverter, is cheap and works, but it may not meet permit requirements.

General information only. Check local laws, your county extension office and manufacturer instructions before you start.

Disclaimer: This page is general educational information, not legal, medical or engineering advice. Composting toilets and the handling of human waste are regulated by state and local health departments, and rules differ widely; check with yours and follow the toilet manufacturer's instructions.