The Smoke Test
In applying the smoke test, a machine designed for the purpose of producing a heavy volume of black smoke is used. Various materials are used in this machine for producing the smoke, among them being oily cotton waste, tarred paper, and oakum which has been soaked in petroleum. Waste is the best material, as it gives off a dense smoke and is not so inflammable as most other materials. Generally the hose connection from the smoke machine is run through a lead cap which is closed up with putty.
After the whole system is filled with smoke, an air pressure equal to a one-inch water column is applied. Defects are shown by puffs of smoke escaping through them.
The alternate is a Smoke cartridge placed in the main sewer line in the basement. Use a wet heavy rag to seal the drain below the access port. Activate the smoke cartridge.
The smoke test appears to be displacing the peppermint test, and for work in general, it appears to be the more reliable of the two but requires specialized equipment.
The Peppermint Test
If the final test is to be made with peppermint, a mixture of 2 ounces of oil of peppermint to a gallon of hot water is the requirement for an ordinary house.
The peppermint should be poured into the roof opening and the opening sealed. The person who has handled the peppermint should not enter the building until the test has been completed, as the odor which he carries will spread about the house.
Peppermint has a very penetrating odor, and its fumes quickly reach every part of the system, and by their escape bring attention to defects. A great point against the use of peppermint is that through a large defect the peppermint will pour in sufficient quantity to quickly fill the house with the odor, making it difficult to locate other leaks. Under certain conditions, however, the peppermint test seems to be the more reliable.
For instance, on old work, much of the soil piping is often buried underground. In the event of defects underground, the peppermint fumes will often penetrate through into the cellar, whereas smoke would not.