Soil-pipes are pipes receiving discharges from water-closets and slop-hoppers, and sometimes from urinals, and, like Goldsmith's bed and chest of drawers, they pay a double debt, being in most cases used also as drain-ventilators. They ought not to be made to serve as rainwater-pipes, as such an arrangement results in the discharge of foul air under the eaves, whence it will in most cases find its way into the building through defective beam-filling or through adjacent windows. The ventilating action of the pipes is also seriously reduced in wet weather, if not entirely stopped, and in winter there is a danger of the pipes being choked with snow or ice. Nor ought soil-pipes to be made to receive the wastes from any other kinds of fittings than those mentioned above.

Ventilation - Every soil-pipe, whether used as a drain-ventilator or not, ought to be carried up full-size to "such a height and in such a position as to afford, by means of the open end of such soil-pipe, a safe outlet for foul air." Many hard-and-fast rules have been laid down as to the distance between the open end of a soil-pipe and the nearest windows, skylights, chimneys, etc, but like all Draconian laws, they are more honoured in the breach than in the observance. Some Sanitary Authorities have a by-law to the effect that the top of the soil-pipe must be above the highest part of the roof of the building to which the pipe is attached; this, in many cases, involves bends both at the eaves and ridge, and these bends seriously diminish the air-extracting power of the pipes, and also retard the inrush of air which is so necessary for the prevention of trap-siphonage. A certain amount of latitude ought to be allowed by Sanitary Authorities, and a little common-sense brought to bear in each case. If the drains are short and self-cleansing and disconnected from the sewer, the air in the soil-pipe will never be very foul, as the sewage will not have time to decompose before it has passed the disconnecting trap. In such cases there would be no danger in terminating the soil-pipe a little above the eaves even if this were only 3 ft. or 4 ft. above the nearest window and about 6 ft. distant from it. If, however, the soil-pipe is also a sewer-ventilator, or if the drains are long and foul, the greatest possible distance ought to be interposed between the soil-pipe and the nearest opening.