Coming to drainage, we will start from the outfall into the main or public sewer, and deal with the drains, water closets, baths, lavatories, sinks, and other apparatus in connection therewith, calling attention to those points requiring special study, whether the system be in connection with a common sewer, cesspool, or scheme of irrigation.
It may be stated at the outset that, wherever practicable, it is always advisable to intercept, or disconnect, that portion of a dwelling in which the sanitary conveniences are placed, from the main block of the house, by a lobby having a cross current of air constantly circulating through it.
It is generally acknowledged by most sanitarians that the house sewer should be disconnected from the public sewer or cesspool by some properly devised trap placed as near the end of the house system as possible, as house sewers not so disconnected allow the free admission of any fever germs which may have found their way into the public sewer from some contaminated source. Otherwise householders would have to rely entirely upon the internal fittings of the house for their protection; and in such cases as (1) the temporary removal of a water closet for repairs, without sealing the pipe end; (2) an accident to a trap, causing the water to run out; or (3) the unsealing of a gully during cleaning operations or the evaporation of water during a dry season (all of which may occur in the average dwelling), the inmates would be exposed to the risk of these germs gaining admission to the house - a risk too-serious to be contemplated or permitted.
The various kinds of traps (a trap being an appliance devised to prevent the rising and entrance into the house of sewer gases by the water which it contains) in use for this purpose of disconnection are too numerous to mention, the main point being that they should be constructed so as to have a dip at the outlet, shown at A, Fig. 991, to allow the standing water in the trap to be more forcibly acted upon by the discharges down the house sewer, so that the water may be properly changed. The body of the trap B should also be reduced to allow of a better seal being obtained (of, say, 2 or 3 inches), without having too large a body of water to resist the flush through it, and of course such reduction must be kept within reasonable limits, or the trap would be liable to choke by solid matter passing down the sewers; and it is very desirable that there should be an inspection arm on the trap, as Fig. 992, to allow of any obstruction in the drain below being removed.
These traps should be placed below a brick-built chamber, as Fig. 999, so that the trap itself can be easily and conveniently cleansed, when required; while the open cover can be utilised as an inlet to ventilate the house drain above, as shown, all possibility of sewer gas arising being obviated by the trap; and when there is an inspection arm, it should be securely fixed, that the joint may be absolutely air-tight.