Oatey Sure-Vent Air Admittance Valve Wall Box with Metal Vent Cover 39010 - The Home Depot
AirCore - Titon UK
What is black hole ventilation? - TheGreenAge
Ø 100mm / 4 inch Wall Ventilation Set - Tumble Dryer Vent Kit - Passive Ventilation Unit with Adjustable Airflow and Three Air Vent Covers : Amazon.co.uk: DIY & Tools