A coupling has a housing which defines a vacuum chamber and, at least in part, a nozzle chamber. The nozzle chamber forms a valve chamber, an intake chamber, and an outlet chamber. A main valve is in the valve chamber. The main valve is movable between an open and closed position. A poppet valve is in the outlet chamber. An air outlet opens from the vacuum chamber into the nozzle chamber. An opening of an air uptake conduit opens into the vacuum chamber. The air outlet opening is distinct from the opening of the uptake conduit. When the main valve is in the open position the valve chamber is open to the outlet chamber and the outlet chamber is open to the intake chamber. In the closed position, the valve chamber is sealed off from the outlet chamber and the intake chamber is sealed off from the outlet chamber.