Used at the base of the chimney system, tees provide access for cleaning at the bottom of the vertical run. All pipe lengths and flue gas carrying components are joined together by a twist lock, bayonet system. The system should be installed with the visible male collar pointing upwards, this is reaffirmed by the directional arrow pointing upwards, indicating the directional flow of flue gases. Taping of joints is unnecessary. B Vent is for atmospheric appliances which have negative pressure flues meaning that when the system is primed and running at normal operating temperatures, air is drawn into the flue via the joints, assisting safe evacuation of flue gases.