I'm having a conservatory built. All my plumbing is being moved except for the vent stack. I won't need it to vent pipes, but it's venting a drain also used by nearby properties. The builders have cut the vent stack to approximately 2 feet above ground level. My question is: Should they have relocated it, as it'll now be in the conservatory? I understood vent stacks were for releasing gasses but the builders informed me it's a fresh air vent.