Characteristics of sewage 1 Protection of water sources from household wastes 2 Septic-tank systems 2 Operation of a septic tank system 2 Selecting the site 4 The house sewer 4 The septic tank 8 Building a concrete tank 11 The effluent sewer 13 The disposal field 13 Disposal methods in tight or wet soils 14 Care and maintenance of septic tanks 17 Effect of drain solvents and other materials 17 Protection against freezing 17 Septic-tank troubles 18 Grease traps 18 Disposal of drainage from fixtures other than toilets 19 Cesspools 20 Privies 21 Care, and maintenance 22 Chemical closets 24 Disposal of garbage and trash 25 TO INSURE healthful living, domestic wastes must be disposed of. Primitive wanderers and too often present-day tourists deposit their wastes promiscuously and move on when the surroundings become foul. This is impractical in built-up communities. Therefore, in most cities and in some rural areas sanitary codes regulate the disposal of wastes. CHARACTERISTICS OF SEWAGE Household sewage ordinarily consists principally of human excrement, toilet paper, garbage, dish water, and other wash water from the various plumbing fixtures and floor drains. Many kinds of bacteria, at times disease-producing ones, are contained in the discharges from the human body. Epidemics of typhoid fever, dysentery, diarrhea, cholera, and other water-borne diseases may result from the pollution of the water supply with sewage. Pollution is carried by water moving underground, as well as by water flowing on the surface. This is especially true in limestone regions, where underground channels and rock crevices permit water to flow for considerable distances with little filtering action. Sewage used for fertilizing or irrigating crops[2] may contaminate vegetables or the udders of cows and thus spread disease. Anthrax, cholera, and parasitic worms may be present in the surface drainage from fields and barn lots. It is wise to regard all sewage as dangerous and to dispose of it promptly in a sanitary manner, so that disease germs will not pollute the water supplies or be spread by flies, animals, or man. [2] This subject is discussed at length in Technical Bulletin 675, Sewage Irrigation as Practiced in the Western States.