I want to put in a new soil stack ino the corner of the house but at the top of the stack there is a dormer window within 1/2m. I wanted to fit a tile vent into the roof. do I have to install this vent at least 900mm from this window, if so can this be done via flexable piping from the soil stack to the tile vent. This would probably be about 1.5m at 45 degrees.