A composting toilet uses no water and is not connected to a septic or sewer. Liquids and solids are separated; solids compost in a sealed bin with peat moss or coconut coir as a bulking agent. For off-grid cabins, tiny houses, RV upgrades, and properties where a septic system would cost $25,000+, it's the practical answer — but only after you understand exactly what the day-to-day operation looks like.

How a composting toilet actually works

A diverter at the front of the bowl routes urine to a separate tank (typically 2.2 gallons on a Nature's Head, 1 gallon on an OGO). Solids drop into a larger composting chamber below, where a hand-crank or motorized agitator stirs them with peat or coir twice a day. A 12-volt or AC fan vents the chamber continuously, exhausting through a 2" or 4" duct to the outside. The smell, when properly operated, is essentially zero — better than a poorly maintained flush toilet because there's no anaerobic septic odor.

What you actually have to do (the daily reality)

Empty the urine tank every 2–4 days for a two-person household. Either into a flush toilet, a graywater system, or diluted 8:1 with water as garden fertilizer. This is the #1 thing nobody mentions in product listings — it's the most frequent operation.
Crank the agitator a few turns after each solid use (or set a daily reminder if your model has a motor)
Empty the solids chamber every 4–8 weeks for two people. Contents look and smell like wet garden mulch by then — not waste. Bury, compost further off-site, or bag for trash depending on local regulations.
Top up the bulking agent (peat moss or coconut coir) — about $20/year per toilet

The four brands worth considering in the US

Nature's Head ($1,050) — the segment leader. Hand-crank agitator, removable solid bin, 12V fan. Easy to live with for one or two users. Built in Ohio. ~5-year typical service life of seals before resealing kit needed.
OGO Origin ($1,100) — newer competitor (2020). Electric agitator at the press of a button, modern industrial design, smaller footprint. Better for tiny-house aesthetics. Reliability data is still being established.
Sun-Mar Compact / Excel ($1,400–$2,200) — Canadian brand, the original mainstream composting toilet (since 1971). Larger capacity for cabins with intermittent heavy use. Uses an internal heating element on AC models to accelerate compost cycles in cold climates.
Trelino Evo ($900–$1,400) — German design, premium build, beautiful but smaller capacity. The "Apple Store" of composting toilets.

Install requirements

Vent duct: 2" or 4" (model-specific), routed through wall or roof. Don't terminate near a window or AC intake.
Power: the fan needs 12V DC (~30 mA — solar-compatible) or 110V AC for full-time models. Tiny houses on solar can handle this trivially.
Floor space: larger than a standard toilet — typical Nature's Head footprint is 22" front-to-back, ~22" wide, 21" tall.
Code: some US jurisdictions require the unit to be NSF-41 certified for permanent residential use; primary-residence permitting is restrictive in many counties. RV, cabin, and accessory-structure use is usually permitted without inspection.

When it's the right answer

Off-grid cabins, tiny houses, RVs replacing failed black tanks, rural properties where the septic-replacement bid is $20k+, drought-zone homeowners reducing water use beyond what a low-flow toilet can achieve, marine and boat installations. Not the right answer for primary-residence bathrooms with sewer access — the operational overhead is real, even if minor.