(3) The connection of a waste pipe of a bath tub with the trap of the water-closet can sometimes be discovered by suddenly emptying the bath tub and watching the contents of the water-closet trap; the latter will be agitated if the waste pipe is discharged into the trap or on the inlet side of trap of the water-closet.
(4) The presence of sewer gas in a room can be detected by the following chemical method: saturate a piece of unglazed paper with a solution of acetate of lead in rain or boiled water, in the proportion of one to eight; allow the paper to dry, and hang up in the room where the escape of sewer gas is suspected; if sewer gas is present, the paper will be completely blackened.
The main tests for plumbing are: (1) the _Hydraulic_ or water-pressure test; (2) the _Smoke_, or sight test, and (3) the _Scent_, or peppermint, etc., test.
The _Water-pressure Test_ is used to test the vertical and horizontal pipes in new plumbing before the fixtures have been connected. It is applied as follows: the end of the house drain is plugged up with a proper air-tight plug, of which there are a number on the market. The pipes are then filled with water to a certain level, which is carefully noted. The water is allowed to stand in the pipes for half an hour, at the expiration of which time, if the joints show no sign of leakage, and are not sweating, and if the level of the water in the pipes has not fallen, the pipes are water-tight. This is a very reliable test, and is made obligatory for testing all new plumbing work.
_The Smoke Test_ is also a very good test. It is applied as follows: by means of bellows, or some exploding, smoke-producing rocket, smoke is forced into the system of pipes, the ends plugged up, and the escape of the smoke watched for, as wherever there are defects in the pipes the smoke will appear. A number of special appliances for this test are manufactured, all of them more or less ingenious.
_The Scent Test_ is made by putting into the pipes a certain quantity of some pungent chemical, like peppermint oil, etc., the odor of which will escape from the defects in the pipes, if there are any. Oil of peppermint is commonly used in this country for the test. The following is the way this test is applied: all the openings of the pipes on the roof, except one, are closed up tightly with paper, rags, etc. Into the one open pipe is poured from two to four ounces of peppermint oil, followed by a pail of hot water, and then the pipe into which the oil has been put is also plugged up. This is done, preferably, by an assistant. The inspector then proceeds to slowly follow the course of the various pipes, and will detect the smell of the oil wherever it may escape from any defects in the pipes. If the test is thoroughly and carefully done, if care is taken that no fixture in the house is used and the traps of same not disturbed during the test, if the openings of the pipes on the roofs are plugged up tightly, if the main house trap is not unsealed (otherwise the oil will escape into the sewer), and if the handling of the oil has been done by an assistant, so that none adheres to the inspector--if all these conditions are carried out, the peppermint test is a most valuable test for the detection of any and all defects in plumbing. Another precaution to be taken is with regard to the rain leader. If the rain leader is not trapped, or if its trap is empty, the peppermint oil may escape from the pipes into the rain leader. Care must be taken, therefore, that the trap at the base of the rain leader be sealed; or, if no trap is existing, to close up the connection of the rain leader with the house drain; or, if this be impossible, to plug up the opening of the leader near the roof.