An infeed device provides a configuration that improves the flow of particulate material into a double wash deck dedusting apparatus. The infeed device is formed with a circular inlet opening, an oval-shaped discharge opening and step sides interconnecting the inlet and discharge openings to prevent bridging in particulate material being fed through the infeed device onto the wash decks. The infeed device can be formed as a separate member that can be inserted into the infeed opening of existing dedusters. The oval-shaped discharge opening is substantially smaller transversely than the diameter of the inlet opening, but has a longitudinal length that is equal to the diameter of the inlet opening and equal to the longitudinal length of the wash decks. The joinder of the wash decks is blunted to eliminate a divider edge on which plastic streamers can hang up while being fed to the wash decks.