Rain-water pipes may be of galvanized wrought-iron, or of tin; when laid inside of a house they should be of cast iron and their joints treated in all respects as those of soil pipes. Before joining the house drain they should be trapped, if such junction is made beyond the main running trap of the drain, and the trap of the leaders should be sufficiently deep in the ground to prevent the water from freezing. If rain leaders join the drain inside of the house they should not have a special trap, unless their top opens near dormitory windows. Sometimes a leader delivers into the main trap of the drain, and thus helps to cleanse the trap.

Rain leaders should never be used as soil pipes nor should they be solely depended upon to ventilate, the drain; and, on the other hand, soil pipes should never be used to carry rain water from th roof. In making a sanitary examination of the Executive Mansion at Washington, under direction of Col. Geo. E. Waring, Jr., the writer had occasion to see an instance of the violation of this rule. The main soil pipe in the building was a 10-inch (!) cast iron pipe, which served the double purpose of receiving the discharge from three water closets, a urinal, a slop sink and some wash bowls and bath tubs, and also all the rain water from the large roof. At each rain-fall this large pipe received ample flushing, but in times of prolonged droughts its inner walls became thoroughly slimed and foul with excremental and other matter. In times of violent rain storms the water rushing down the 10-inch pipe and passing the branch wastes, very likely siphoned all water out of the traps, thus leaving the house unprotected against the foul gases of the soil pipe.