Very long retention times for sewage have the ability to virtually destroy pathogens. The amount of time human excrement should be retained varies. In a very warm climate you may want to retain the waste for 60-90 days, however in cold climates (20 degrees C and below) 150 or more days of retention are recommended. Retention time can be controlled via the biodigester HRT or by holding the effluent for an additional period of time. The option that is the most economic should be considered as well as safety factors such as the access to holding tank and any other issue that involves potential exposure to humans and animals. Safety Warning: Retention methods to destroy pathogens should be confirmed by lab results before adoption.