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least, are not on the level of the ordinary flow of sewage in the main sewer, such tributary sewers, or drains, will be liable to be back-watered, in which case deposit will take place in the length of submerged invert, and so the tributary sewer, or drain, will become choked with its own silt. Many drains are so choked, where all the inverts in a flat district join upon the same level, because the sewage of the main sewer, which is in some degree constant, back-waters the inverts of the tributaries as described, which tributaries are only in use intermittently.
13. Earthenware pipes of equal diameters should not be laid as branches or tributaries, that is, 9 in. leading into 9 in., or 6 in. into 6 in., but a lesser pipe should be joined on to the greater, as 12 in. to 15 in., 9 in. to 12 in., 6 in. to 9 in., and so on.
14. House-drains should not pass direct from sewers to the inside of houses, but all drains should end at an outside wall. House-drains, sink-pipes, and soil-pipes should have ample means of external ventilation. In towns where houses have to be drained from back to front through the basement the drain-pipes should have an effectual joint, and be bedded and covered in concrete, such drains being ventilated, back and front, on the outside of the house.
15. Sinks and water-closets should be against external walls, so that the refuse water, or soil, may be discharged into a ventilated trap and drain outside the main wall. Down-spouts may be used for ventilation, care being taken that the head of such spout is not near a window. Water-closets or sinks fixed within houses, and having no means of direct daylight and
external air ventilation, are liable to become nuisances, and may be injurious to health; and if such sinks and. water-closets cannot be ventilated in an efficient manner they had better be removed.
16. Inlets to all pipe-drains should be properly protected; that is, no pipe-drain should have its upper end exposed so as to admit sticks, stones, or other solid materials being accidentally or mischievously passed in.
17. Side-junctions for house-drains should be provided in all new sewers and drains. The position should be sketched, and indicated by figures in a book or on a plan. Side-junctions not used at once should be carefully closed for subsequent use. If side-junctions are not provided and put in as the sewers are being constructed or laid, the cost of subsequent provision and insertion will be much greater. It will be cheaper to insert extra side-junctions during construction rather than to have pipes to remove or brick sewers to cut after the trenches have been filled in and become consolidated, and the road or street surfaces made good.
18. A record should be kept by the surveyor of the character of the subsoil opened out in each street as it is being sewered or drained. A sketch-book may be used for the purpose, a section being drawn on a page to show the character and variety of the subsoil as excavated in each street or road, the depths of the various layers, as of sand, gravel, clay, rock, or other material, being described in writing and also figured in the diagram; these books to be indexed, and preserved. with the plans for subsequent reference and use.
19. Sewers and drains should be set out true in line and in gradient. All the materials used should be sound, and the workmanship should be carefully attended to. Surveyors who have had but little practical experience in sewer construction do not at once perceive the necessity for straight lines, true gradients, with manholes, or lampholes, at the changes of line or gradient. The reasons will, however, become obvious when the works have been completed, as the surveyor will find that truth of line and of gradient can only be obtained by a use of good material and the best of workmanship; the sewer-trench must have been excavated carefully and must have been shored properly and strongly, the trench must also have been filled in carefully. The manholes and lampholes afford means for ready inspection, as also for flushing and cleansing; and, as previously stated, the line of the sewer can be readily and accurately indicated upon the surface of the street or road, and the exact position or depth of every side-junction be found. In main streets having much traffic, "side entrances" may have to be used instead of manholes. Each manhole may be a "flushing chamber," and each manhole and lamphole may also be a sewer ventilator. Sewers and drains which
have been set out and constructed true in line and in gradient are, for all subsequent time, under the ready inspection of the local surveyor.
20. "Sight-rails" should be put in each street before the ground is opened out, showing the centre line of each sewer and depth to the invert. The proper use of sight-rails in sewer and drain construction, when put up by the surveyor, will enable the
foreman to set out and excavate the trench truly. These sight-rails should be strong, and should also be securely fixed on firm ground; that is, beyond the influence of the excavation to be made, and if the sub-strata is peaty, or such as will shrink under pumping, to lower the subsoil water, care must be taken that the sight-rail or bench-mark to be worked to is in such position as to remain unaffected, or the result will be a crippled sewer, that is, the grade and line will not be true.
21. Sewers having steep gradients should have full means for ventilation at the highest points.
22. Tall chimneys may be used with advantage for sewer and drain ventilators, if the owners will allow a connection to be made.
23. Sewer-outlet works should be simple in form, cheap in construction, and so arranged as to remove all solids, sediment, and floculent matter from the sewage. Some diagrams of works of this character will be found at the end of these "Suggestions."
Inspection manholes should always be constructed at the front and back of each house to facilitate the regular inspection and cleansing of the house-drains. By this arrangement the drains are placed under such control as is unattainable by other methods of construction.
Students desiring information as to formation of streets, and town surveyor's duties, should peruse the book "Sanitary Engineering," by H. Percy Boulnois, Borough Engineer, Portsmouth.
LEGAL PROCEEDINGS AND REPORTS.
In all matters where an opinion upon a legal question is required, it will be clearly understood that the clerk to the sanitary authority, who of course is nearly always a solicitor, is the proper person to seek advice from, but it may be as well to explain that my motive in making remarks on this subject is that there are always many little matters in an inspector's practice in which he will be called upon to give opinions without having an opportunity to consult the clerk, and as a rule clerks cannot be troubled with so many matters, unless of great importance.
In making out forms, notices, and other documents under the Acts, great care should be exercised in following as closely as possible the exact wording of the Act.
It will be necessary on an inspector entering upon a new (country) appointment, to direct the attention of the committee to the 259th section of the Public Health Act, 1875, and have a resolution on the books authorizing him to appear in prosecutions on their behalf, presuming that the same method is adopted as is carried out in most large towns, namely, that the inspector conducts his own sanitary prosecutions,