An air seeder distribution apparatus has a manifold and a plurality of delivery conduit connected to ports of the manifold. A supply conduit carries a product air stream and is connected the manifold interior. A port valve when open connects a delivery conduit to the manifold interior through the port and disconnects same when closed. A purging conduit connects the supply conduit, at a clean air location configured to receive from the supply conduit a clean air stream with no agricultural products entrained therein, to the delivery conduit such that the clean air stream has an open path from the supply conduit to the delivery conduit. When the port valve is open the clean air stream flows through the purging conduit at a low first flow rate, and when the port valve is closed the clean air stream flows through the purging conduit at a second significantly greater flow rate.
