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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 Portland 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 regulation No. 12 of these regulations, no drain or sewer shall be larger than is neces- sary 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 re- maining 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 a quality to be approved by the Build- ing Authority and the joints shall be properly caulked and run with lead, and (unless the written permission of the Building Authority has first been obtained to lay the drain or sewer otherwise) shall be laid in one straight line for the whole distance beneath such build- ing, and shall be imbedded and encased throughout its entire length in four inches of concrete as specified in regulation No. 10 of these regulations.
18. Whenever a covered drain or sewer traverses soft or yield- ing ground, or when water may make its appearance in the trench, the drain or sewer shall be surrounded throughout its entire length with not less than four inches of concrete as specified in regulation No. 10 of these regulations.
19. No drain or sewer shall be constructed in such manner as to allow any inlet to such drain or sewer to be placed inside any roofed building, (except such inlet as may be necessary from the apparatus of any water closet or urinal):
Provided that, if in the opinion of the Building Authority it is impracticable to comply with this regulation in respect of any pre- mises without encroaching on unleased Crown land, the Building Authority shall, on payment by the owner of such premises of a fee of twenty dollars, construct an inlet on Crown land to receive the drainage of such premises and connect such inlet with a sewer. The cost of cleansing and maintaining such inlet shall thereafter be borne by the owner for the time being of the said premises, and may be recovered by the Building Authority from such owner by an action in the Supreme Court in its summary jurisdiction.
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