_Extension of Vertical Pipes._--By the main trap the house-plumbing system is disconnected from the sewer, and by the traps on each fixture from the air in the rooms; still, as the soil, waste, and drain pipes usually contain offensive solids and liquids which contaminate the air in the pipes, it is a good method to ventilate these pipes. This ventilation of the soil, waste, and house drain pipes prevents the bad effects on health from the odors, etc., given off by the slime and excreta adhering in the pipes, and it is accomplished by two means: (1) by extension of the vertical pipes to the fresh air above the roof, and (2) by the fresh-air inlet on the house drain.
By these means a current of air is established through the vertical and horizontal pipes.
Every vertical pipe must be extended above the roof at least two feet above the highest coping of the roof or chimney. The extension must be far from the air shafts, windows, ventilators, and mouths of chimneys, so as to prevent air from the pipes being drawn into them. The extension must be not less than the full size of each pipe, so as to avoid friction from the circulation of air. The use of covers, cowls, return bends, etc., is reprehensible, as they interfere with the free circulation of air. A wire basket may be inserted to prevent foreign substances from falling into pipes.
_Fresh-air Inlet._--The fresh-air inlet is a pipe of about four inches in diameter; it enters the house drain on the house side of the main trap, and extends to the external air at or near the curb, or at any convenient place, at least fifteen feet from the nearest window. The fresh-air inlet pipe usually terminates in a receptacle covered by an iron grating, and should be far from the cold-air box of any hot-air furnace. When clean, properly cared for, and extended above the ground, the fresh-air inlet, in conjunction with the open extended vertical pipe, is an efficient means of ventilating the air in the house pipes; unfortunately most fresh-air inlets are constantly obstructed, and do not serve the purpose for which they are made.
=The Soil and Waste Pipes.=--The soil pipe receives liquid and solid sewage from the water-closets and urinals; the waste pipe receives all waste water from sinks, washbasins, bath tubs, etc.