This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
Drains are tested with either scent, smoke, or water. In the first, strong-smelling and volatile liquids are poured into the drains, defects in which may be revealed by the after-occurrence of the scent in rooms or cellars. Sanitas, carbolic acid, or paraffin will answer the purpose, but peppermint and other expensive scents are often used. The inspector, however, usually uses either smoke or water in making his tests.
The smoke-teat is applied by forcing into the drain a pungent smoke, either from a rocket-case filled with a pyrotechnical compound, or a "smoke-machine " burning cotton waste.
It was once said to the writer, by an author of books on sanitation, that the smoke-test is useless, and not worthy the name of test. This is a very unfair statement, and carries with it no conviction of having been made from practical day-by-day and all-round experience. If properly applied, it will discover nine faulty drains out of ten, and to the experienced inspector will give some suspicion of the remaining one, which, at a subsequent trial, under different atmospheric conditions, may be resolved into proof. The worst that can be against the smoke-test is that, in a list of (say) 1000 drains, 995 of which are Bound, it may discover the five faulty ones, but leave the inspector in doubt about the others, and the inspector must enter these in his book as "in good order", when he has only the negative fact of "no results" to support his record.
1 See Fig. 355, page 455, vol. i.; an alternative arrangement is shown in Fig. 356, page 456, vol. i. - ED.
The smoke-rocket is a very useful article, as three or four of them can with ease be carried about by the inspector on his ordinary rounds, for application as a sort of " first aid ". It affords a simple test, and often discovers a fault, thus rendering more elalborate efforts unnecessary.
The rocket is usually applied at an emptied gully-trap or other drain-inlet, and burns for about five minutes. When one is exhausted a second may follow, but here a word of warning is necessary. If the drain at the exposed part is full of dense smoke when the first rocket or smoke-case is withdrawn, the second must not be applied until the smoke has cleared away, or an explosion may occur - a slight one, perhaps, but suffi-cient to injure the hand which holds the second rocket, or the head which may be over the sink. In the old-fashioned "cesspool" gullies, the rocket can, when well alight, be passed into the water and pushed up to the outlet without being extinguished; it is well to know this, as the emptying of gullies is not always a pleasant job. It may be necessary to flatten the mouth of the rocket under the inspector's heel, in order that it may enter the drain more easily.
It has often occurred to the writer that the plunging of a fiery rocket into an earthenware gully, drain-pipe, or w.c.-trap, would be likely to cause fracture, but he has not seen any instance of this. Having regard to this possibility, however, perhaps the best way of using the rocket is to inclose it in a metallic sheath or box, to one end of which is attached a brass pipe, long enough to allow a rubber tube to be slipped on the end without being in danger from the heat. The free end of this tube (see Fig. 671) can be passed through the first removing the water with a ladle or syringe, and replacing it when all is in position. It may not even he necessary to remove the water, as a sharp blast from the inspector's mouth, applied to the rocket-end of the rubber tube before attaching the rocket-case, will easily remove the water which enters and lodges in the bent part of the tube as it is passed through the trap. Another sheath, made by the writer for application to gullies, is shown in Fig. 672, and consists of a case similar to the last, but the projecting tube is longer and bent horseshoe-like, no rubber being used. This in-strument, with the lighted rocket in it, is simply passed down through the water in the gully, and hooked up under the trap, so that it is not neces-aary for the inspector to touch the sewage. It is tied up in this position - from an "eye" brazed on to its side - to a spout or water-tap. The rocket will blow out all the water in the bend. Smoke-machines are of three forms, each forcing air into the drain through burning cotton waste. One has a fan-blast, worked by turning a handle which drives the fan; another contains a leather bellows fixed in a box by the side of the waste-container, and worked by moving an upright handle to and fro. Both these are very useful and powerful machines, but they are too cumbersome for the ordinary work of the inspector. The beat compromise is the third form, which consists of a water-seal bellows; and among the best of these is that shown in Fig. 673, and made by a Newcastle firm in accordance with the writer's suggestions. This apparatus is not patented, and the cost of one will probably not exceed £2, whilst as much as £5 may be asked for patented, but possibly inferior, appliances.
Fig. 670. - Section of Old-fashioned "Cesspool" Gully.
Fig. 671. - Sheath and Tubes for Smoke-rocket gully or w.c.-trap,.
In applying the smoke-test, those parts of a drainage-system, the ends or heads of which are closed by traps, such as branches and unventilated soil-pipes, may. if sound, not be permeated with smoke. It is necessary, therefore, before commencing, to draw all the traps, w.c. traps included, and to restore the seal immediately on the appearance of smoke. This will not only ensure every part being brought under the full influence of the test, but will tend to remove doubts that might Otherwise arise as to the efficiency of the examination. Where possible, the vent shafts must be closed as soon as the smoke is seen to issue.
Fig. 672 - Sheath with Bent Brass Tube for Smoke-rocket.
Fig. 673. - Section of Smoke-machine for.
Testing Drains. a. Performed tray for cotton waste.