As per SANS 10400 – P ,Ensure your installation is done correctly as per the following key points
A ventilating pipe or two-way vent valve shall be so installed that its open end is…
1. Not less than 2.5m above finished ground level
2. Not less than 100mm above the closest part of the roof covering of the building through which it passes.
3. Not less than 2m above the head of any window or door
4. Not less than 2.5m above the surface level or any roof slab, where the slab may at any time be occupied by people.