Composting toilets are designed to stop the waste of water that the typical toilet can use in a day. It is not environmentally or financially smart to treat water for drinking and then to use it for flushing waste. The simple design of the outhouse was created originally when water was not accessible for flushing. You can use the outhouse waste as compost if you handle it properly.
Collect the waste in a container that will not leach water into the soil. This can be as simple as a 5-gallon bucket placed strategically in the outhouse. The old practice of digging a hole in the ground is no longer used since harmful bacteria and viruses can migrate into the soil and drinking water, according to the nonprofit Appalachia-Science in the Public Interest (A-SPI).
Place 4 inches of the organic material into the bottom of the container to start the composting process. Keep a fresh supply in the outhouse and add a quart of the organic material to be used as a dry flush after each use. There is no need to add water since most of the waste is composed of water, says A-SPI.
Set up a secondary composting container. This needs to be protected from rain, from ground water, from animals or insects. It needs to be big enough to hold a cubic yard of composting material. This is the size at which enough heat is produced to compost the waste and kill most of the harmful pathogens that can be carried in human waste. The initial collection container should be dumped into this compost for final decomposition.
Keep the carbon to nitrogen ratio high in your secondary compost by adding plenty of organic material like peat moss, wood chips, sawdust or straw. Do not add lime or ashes as it will alter the acid balance, keeping the pile from decomposing properly. Turn the pile every month until the heat has dissipated.
Use the finished outhouse compost in your yard as mulch for everything except vegetables. There is a possibility that certain viruses can still be present and will be taken up by vegetables.