Already very good suggestions ...

Already very good suggestions have been offered. One that is still missing is known as ROOT ZONE TREATMENT. It works on the principle of pre treating sewage in a septic tank or Imhoff Tank and allowing the effluent to flow laterally through a natural or prepared bed of soil over which plants like reeds are planted on normal top soil. The roots of the plants and the soil removes organic matter from the effluent which comes out clean and odourless at the other end. It can be used for any purpose other than drinking.