Drain Vent Pipe
A Vent Pipe is installed through the roof to allow sewer drains to breathe and prevent noxious gases entering the house.
WIKIPEDIA ENTRY DRAIN WASTE VENT SYSTEM.
From the first phone call to the report Abis were excellent. They turned up to the appointment on time, there were no hidden costs, the report was easy to read and even had pictures! I would recommend Abis every time!