(1) Trapped gullies shall be so formed and installed as to maintain a water-seal of 60 millimetres, and no other trap shall be placed between a trapped gully and the public sewer.

(2) Gully-traps and grease-traps shall be provided with hopper-heads with side and vertical inlets to receive waste-pipes.

(3) A hopper-head shall be encased in cement concrete at least 75 millimetres thick, which shall be carried to a height of at least 150 millimetres above the surrounding ground-level.