(fig. 25) the branch drains also may be made to discharge by means of short curved channel pipes emptying over the main channel. Winser's curved channel pipes. should be used when connected with a high soil-pipe. By this system of manhole chambers, the drain-which runs in a straight line from manhole to manhole-can be inspected and cleared of deposit or obstructions without breaking into it. Where it is necessary to connect a small pipe with a larger pipe, the junction should always be effected by means of a taper or diminishing pipe.

The disconnection of the house drain from the public

FIG. 25.-Plan of Inspection Chamber for House Drain, where it changes its direction.

sewer is a matter of the greatest importance, experience having proved the absolute necessity of preventing the entry of air from the common sewer into any part of a house or its drainage arrangements. Disconnection is effected by interposing a siphon trap between the house. drain and the sewer, and advantage is taken of this break to provide a means of inlet for fresh air into the house drain at this point. The point usually chosen for disconnection is where the house drain leaves the premises, and before its junction with the sewer. If the house drain is provided with a ventilating pipe at the

further end, air, admitted on the house side of the disconnection trap, will produce a current from the lower opening to the higher, and constant circulation will thus be established in the drain and soil-pipe, preventing any accumulation of foul air.

The simplest form of disconnecting apparatus consists of a siphon trap with fresh air inlet, formed of stoneware pipes. There are several varieties of this sort of trap sold, under the names of "sewer-airinterceptor," "sewer-air-trap," etc. The points to be observed in choosing a trap of this description, are:(1) where the drain is a 6-inch or 9-inch pipe, the siphon should be a size smaller than the drain; (2) there should be a fall of an inch or more from the level of the discharging end of the house drain to the surface of the trapping water; (3) the siphon should provide an adequate seal of 2 or 3 inches of water; (4) the inlet to the siphon should be nearly vertical, whilst the outlet rises at an angle of not more than 45°. These qualities, except (3), are necessary to ensure efficient flushing of the trap; and to further attain this end, the drain should be laid with a slightly greater fall before its junction with the trap. The inlet to the siphon is continued up by a vertical pipe to the surface of the ground, and there covered by an open iron grating, to provide the necessary inlet for fresh air.

In larger houses it is now usual to provide a disconnection manhole chamber (fig. 26), instead of the simple trap above described. This chamber is built of glazed brickwork in cement upon a bed of concrete. The drain is continued through the floor of the manhole in the form of a glazed channel pipe, from which the floormade of cement-slopes up at an angle of 30° to the brick walls of the manhole. The branch drains, in the

form of suitably curved channel pipes, are made to discharge over the main channel, which itself discharges into a siphon trap. The siphon trap should be provided with a "raking" arm, one end of which opens into the manhole, the other end being connected with the drain beyond the trap. This arm is to permit of obstruction being removed from the drain between the siphon trap and the sewer; when not in use, the manhole end should be closed with a tile set in cement. The manhole chamber may be closed above by an air-tight iron cover; and the fresh air should then be admitted into the chamber by a 6-inch pipe, the manhole end of the pipe being opposite the entrance of the drain, whilst the end open to the air is covered by an iron grating. Where the disconnection chamber is some distance from the house, fresh air may be admitted by perforations in the iron cover. The chief advantage of the manhole chamber is the readiness with which the drain can be inspected and cleansed.

Where the house drain discharges into a sewer liable to flooding, it is necessary to provide a tide valve between the sewer and drain. The best form of this apparatus is a floating ball valve in an enlargement of the drain, which rises, on the sewage being backed up from the sewer, and closes the outlet to the drain.

For house drains with insufficient gradient, in which deposit is liable to occur, it is advisable to place an automatic flush tank at the head of the drain; by this means the dangers arising from insufficient fall may be to a great extent obviated.

A simple

When a house drain has been laid, and before it is covered in, it should be tested for leaks. method is to plug the lower end of the drain with water. If after standing some time the

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and fill it level of

the water at the upper end is found to descend, the drain is not water-tight and the joints should be examined for leaks. Another method, which tests the soil-pipe as well as the drains, is to burn brown paper or some sulphur in a shovel in the disconnection trap or chamber, the airinlet being closed as soon as the paper or sulphur is well alight; or the drain may be filled with smoke by a forcing apparatus actuated by an air-pump, or by firing smoke rockets into it. Leakages in the drain or soilpipe will then become evident to both sight and smell. A third method, which is especially applicable for testing drains and soil-pipes which have been long in position, and in which there is no disconnection apparatus, is to pour down the ventilator to the soil-pipe, if there is one, or in default, the highest water-closet, about half an ounce of oil of peppermint, following it up with several gallons of hot water. By this means the smallest leak will be discovered by the sense of smell, as the peppermint is excessively volatile. Soil-pipes and their branches may be tested before the W. C's. are connected, by soldering over the apertures where the traps of the W. C's. are connected with the soil-pipes, and then filling the pipes with water. This is a severe test owing to the great head of water, but 3-inch lead pipes (9 lb. to the square foot) are found to stand the test well if the joints are well made.

All waste pipes from baths, lavatories, sinks, and safetrays under water-closets, must be disconnected from the drain or soil-pipe by being made to discharge into the open air. The waste pipes from baths, lavatories, and sinks should be of large diameter (1 or 2 inches) to ensure rapid emptying of the baths, sinks, etc., and as short as possible; for they tend to become coated internally with a deposit of dirt and soap, which decom