(1) All sewers shall be of a size capable of tanking the discharge into them, calculated in accordance with the relevant provisions of this chapter, with a minimum internal diameter of 100 millimetres.

(2) Sewers of 100-millimetre and 150-millimetre diameter shall be laid with gradients lying between a maximum of 1 in 10 and a minimum of 1 in 60:

Provided that the local authority may, in its discretion, allow the maximum gradient to be increased or the minimum gradient to be increased or the minimum gradient to be decreased in particular circumstances, taking into account available falls, type of pipes and joints used and the flow anticipated in the pipes.

(3) All sewers shall be laid in true alignment and at uniform gradients, and shall be so supported or so anchored as to maintain these gradients.

(4) All spigot-and-socket sewer pipes shall be laid with the spigot-ends pointing in the direction of the flow.

(5) All sewers shall be laid so that the barrel of the pipe is fully supported and evenly bedded on the bottom of the trench or on any special bed provided.

(6) The backfilling to all sewers shall be carried out by carefully placing and consolidating sand or selected fine granulated soil evenly around the pipe on bot sides, and on top of the pipe to a height of 150 millimetres above the crown of the pipe, and thereafter backfilling and consolidating the remainder of the trench up to the final level.

(7) Changes in the horizontal direction of sewers shall be made with bends of approved materials, which shall have radii not less than those specified in C.A.S. No A16 for earthenware bends.

(8) When the change of direction of flow does not exceed 90 degrees, the radius of the complete bend shall be not less than three times the internal diameter of the pipes.

(9) When the change of direction of flow is more than 90 degrees—

a) a series of bends shall be installed, each of which shall comply with the fore-going requirements of this section; or

b) the change of direction of flow may be made within a manhole with channel bends complying with the requirements of C.A.S. No. A16.

(10) Should channel bends of any approved material other than earthenware be used, these channel bends shall have radii not less than those specified for earthenware channel bends.

(11) Any change in the vertical direction exceeding 5 degrees or a sudden drop in invert level of 300 millimetres or more in a sewer shall be made with square or ramp junctions or bends the dimensions of which shall comply with C.A.S, No. A16.