A seed flow chamber for handling seed and grain commodity, especially for use with a seed treatment applicator. Seed flow is received through an upper inlet opening configured to receive a flow of seed and discharged through a lower discharge opening. A diverging guide member splits the seed flow. A converging guide member disposed below the diverging guide member reunites the seed flow prior to discharge. The converging member has a downward sloping surface and an air vent, such as a plurality of airflow apertures connected to a plenum. The air vent is configured to communicate with an air supply. A vacuum vent—disposed below the diverging guide member—is configured to communicate with a vacuum source. A fan system recirculates air between the air vent and the vacuum vent. Dehumidifier may condition the air supply to assist with drying.