After completing an installation, you should test it for any defects in workmanship. These tests are made twice during installation. When the roughing-in has been completed, either an air or a water test is made. Later, when the fixtures are in place and the system is ready for use, either a smoke or a peppermint test is made. The test will reveal any wrong connections, loose fittings, and so on.
All outlets except one at the highest point in the system are capped or plugged in preparation for the roughing-in test. Test plugs, which are easy to remove when the test is over, are usually used to seal the openings in the pipe.
Close all openings down to the lower end of the house drain and fill the pipes through the highest opening (this is usually above the roof) until the entire system is filled with water. If an examination of the waste and vent piping reveals no leaks, the system will pass inspection and the fixtures may be safely installed. One objection to the water test, however, is the fact that the pressure exerted by the water is not uniform throughout the system.
The pressure is great at the bottom of the system but relatively insignificant at the top. It is also dangerous to make the water test in freezing weather since there is a real possibility that the oakum in leaded joints will become saturated and freeze. As a result the joints may be forced out of their hubs.
Air tests are applied by closing openings and pumping air into the system until a uniform pressure of five pounds registers on a gauge. The system is kept at the same pressure for time and then tested again. Any drop in the pressure indicates a leak in the system. The air test has two principal advantages.
It can be made in freezing weather, and it subjects the entire system to a uniform pressure. On the other hand, it does not indicate location of the leak. Consequently, unless the leak is a big one, it may be difficult to find. A soapy lather applied to all joints with a brush will reveal leaks by forming bubbles wherever air is escaping.
The final test, with fixtures in place, can be made with either smoke or peppermint. To make the peppermint test, seal all traps with water and all openings with caps or plugs. All windows and doors should be closed tightly in order to aid in the detection of leaks. The system is partly filled through its highest point with a solution of hot water and oil of peppermint. The tester should avoid getting oil of peppermint on his hands or clothes.
To detect the leaks, he will have to be entirely free of its odor. After solution is added, the system is capped and allowed to stand for a short time. Then the tester goes over every joint, fixture connection, and trap. Wherever he detects the odor of peppermint, there is a leak. Note that the system needs to be only partially filled with the oil and hot water mixture as it vaporizes and so reaches all points.
The smoke test requires the use of a smoke machine. All lower openings in the system are sealed, but the roof openings are left uncapped. Smoke is then pumped into the system until a considerable volume of it is seen issuing from the roof openings. Then they are capped. The machine continues to force smoke into the piping until a pressure equivalent to a rise of one inch in a water column gauge is reached. At this point, check all connections for signs of smoke. The principal objection to the smoke test is the possible damage it might do to interiors in the case of a line break.
Make either the peppermint or the smoke test on old piping. The peppermint test is preferred because it can be detected in places, such as underground piping, where smoke cannot. As these tests are usually made in the presence of a local building or public health inspector, you should pre-test all connections before calling him in. You should also remember that excessive pressure in either the smoke or the air test will blow out your trap seals, defeating the entire purpose of the test. To avoid this, take care to use only recommended pressures.