(1) In the one-pipe system, the water-seal of the trap of every waste-water fitting shall be protected by means of an anti-siphon pipe :

Provided that, where horizontal waste-pipes are back-vented as described in section 46, the anti-siphon pipes may be omitted.

(2) In the one-pipe system, the water-seal of the trap of every waste-water fitting shall be protected by means of an anti-siphon pipe of a back-vent unless an approved resealing-trap is installed:

Provided that this subsection shall not apply in the case of a single bath, shower or sink having an independent discharge to a gully, and where the total length of the waste-pipe does not exceed six metres.