Subject to the provisions of section 46, the water-seal of the trap of a soil-water fitting shall, in the following cases, be protected by means of an anti-siphon pipe of such dimensions and location as are section 40, respectively, that is to say where such soil-water fitting-

a) discharges into an unventilated sewer or soil-pipe or a combination thereof in which there is a fall of more than 1,2 metres within a horizontal distance of 2,4 meters from the crown of the trap; or

b) discharges into a ventilated soil-pipe or private sewer having an inclination from the horizontal of 45 degrees or greater, and which receives the discharge from one or more other soil soil-water fittings at a higher level, except as provided for in section 48; or

c) not being the soil-water fitting situated at the uppermost or remotest end of the soil-pipe or sewer, discharges into an unventilated soil-pipe or sewer which receives the discharge from any other soil-water fitting.