This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol2", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
Where the rain water is collected for daily use, R.W.
tanks should be constructed in brick on a concrete bottom, and the walls inside rendered in Portland cement mortar, 1 to 1, and the top domed over and fitted with a cast-iron inspection cover. In order to keep the water as clean as possible a filter composed of gravel about 1/2 inch diameter should be provided. The bottom of the filter should be kept at least 1 foot 6 inches below the inlet into R.W. tank to catch the sediment brought down in the drains.
After the drains have been laid, and before they are covered with concrete, they should be thoroughly tested.
There are several methods of testing drains, namely:-
Volatile Oil Test. Defects maybe discovered by pouring oil of peppermint or ether and hot water down the highest soil pipe and blocking the pipe and other outlets with a sack. If the odour can be traced from any part a defect exists. This test is not reliable, as defects may exist which may not be discovered by its application.
The Smoke Test. In this test the drains are charged with smoke by means of a rocket or smoke machine which can be applied through the fresh air inlet, ventilating pipe, or gulley from which the water has been removed. An escape of smoke at any part will denote a defect.
The Water Test. The most severe, and at the same time the most satisfactory, is the hydraulic test.
An inflated indiarubber bag or an indiarubber plug is introduced into the drain at the intercepting chamber. The whole drainage system is then filled with water until it rises to the level of a standpipe 5 feet above the highest gulley. This will give a pressure equal to 2.16 lbs. per square inch. If after, say, half an hour the water level has lowered, it shows that a leakage has taken place.
The drains should be tested in lengths from the several inspection chambers. Care should be taken that the drains are not filled from two points at the same time, because an air-lock would occur, and the test would be useless.