Some units also have a mechanism that regularly stirs or mixes the compost. If the vent chimney gets sun exposure, painting it black will increase natural air convection. These systems can be installed in areas where there is no electric utility service. A properly operating composting toilet will produce odorless carbon dioxide, nitrogen, and water vapor. If there is too much moisture or not enough oxygen, anaerobic bacteria, which live without oxygen, will become active.
Anaerobic bacteria produce various gases that give off odors.
This is what occurs in a pit privy or outhouse. Odors from a composting toilet are an indication that the aerobic process is not functioning properly. The size and complexity of composting toilets vary. There are small units available that are not much larger than a standard commode, and are installed wholly within the bathroom. Others use a toilet seat with a drop chute connected to a composting vessel located in the basement, crawl space, or other room under the bathroom.