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9. All covered drains and sewers shall be laid in straight lines and regular gradients between the points at which any change of direction occurs, and all changes of direction shall be made by means of properly curved pipes or by half channels in manholes.
10. Concrete for encasing drains or sewers shall be composed of four parts of good sound clean stone, broken to pass through a one inch ring, two parts of sand and one part of Portland cement thoroughly well mixed and well rammed into place or of such other materials and in such proportions as the Building Authority may approve.
11. Cement-mortar for the jointing of pipes or any other work shall be mixed in the proportions of not more than three parts of clean sharp sand to one part of good Fortland cement and used fresh.
12. No covered drain or sewer shall be less than four inches in clear internal diameter, but the Building Authority may require any covered drain or sewer to be constructed of a larger diameter.
13. Subject to the limitation mentioned in regula tion No. 12 of these regulations, no drain or sewer shall be larger than is necessary in the opinion of the Building Authority to carry off the sewage of the premises drained or the sewage with the rain-water, which, under conditions hereinafter specified in. regulations Nos. 35, 36 and 37 of these regulations, shall be admitted to the drain.
14. Every drain or sewer shall have the maximum fall, throughout its length, that the relative levels of the public sewer and of the most remote inlet will admit of:
Provided always-
(a) that, if the available fall exceeds 1 in 30, the part of the drain or sewer more remote from the public sewer may be laid with a fall of 1 in 30; and the remainder, with such greater fall as may be necessary to connect with the public sewer;
(b) that, if the excavation necessary to obtain. the maximum available fall, is likely in the opinion of the Building Authority to endanger the stability of the adjoining or neighbouring property, the gradient may be modified to such extent as the Building Authority may approve.
15. Whenever the available fall for a covered drain or sewer is less than 1 in 30, the Building Authority may require the gradient of the drain or sewer to be varied by increasing such gradient in the upper portion of such drain or sewer and by reducing it in the remaining portions.
16. Whenever the gradient of any portion of a covered drain or sewer is less than 1 in 30, the Building Authority may require an automatic flush tank or any other suitable contrivance for attaining an effective flush to be provided to his satisfaction.
17. No drain or sewer shall be so constructed as to pass under any domestic building except when any other mode of construction is impracticable. Any drain or sewer passing under a building shall be of cast-iron pipes coated inside with Dr. Angus Smith's patent composition, or of other material approved by the Building Authority, and all such pipes shall be of
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