Venting through the walls of an interior room of a building to an external environment is facilitated by apparatus and techniques for mounting an in-wall unit for interfacing with the exhaust ports of equipment, such as dryers, using flexible pipe. The in-wall unit connects with venting pipe, such as stovepipe, for connecting to the external environment through an exterior surface, such as a roof. If a roof exhaust is desired, a vent assembly is provided that contains a flap that automatically closes when the exhaust flow terminates, but opens when venting is underway. The flap is removable so that cleanout of path between the in-wall unit and the room exhaust can easily occur.