(1) Every soil-pipe, waste-sewer and sewer, including every branch thereof which exceeds six metres in length, measured from its junction with a ventilated private sewer or a ventilated soil-pipe to its point of connexion with the soil-fitting which it serves, shall be provided with a ventilation-pipe leading up-wards from its highest convenient point.

(2) Every waste-pipe and branch waste-pipe which exceeds six metres in length, measures from its point of discharge over a gully or from its junction with a ventilated waste-pipe or ventilated soil-pipe, as the case may be, to its joints of connexion with the waste-water fitting which it serves shall be provided with a ventilation-pipe leading upwards from its highest convenient point.

(3) Subject to the provisions of anything to the contrary contained in Chapter, there shall be at least one 100-millimetre-diameter vent for every private sewer:

Provided that, with the prior approval of the local authority, this vent may be omitted on a sewer of less than six metres in length which receives the discharge from a single soil-water fitting and not more than two waste-water fittings.

TABLE VI

(4) The diameter of a vent and of anti-siphon pipe shall be determined from its length and from the total of discharge units connected thereto as provided in Table VII:

Provided that no vent serving a soil-fitting shall have a diameter less than 50 millimetres.