In the floor of a pulp slurry inlet chamber an opening is provided. The opening is elongate and arranged substantially tangential to the outer, bounding wall of the chamber. Barriers of arcuate cross-section depend from the opening, at opposite ends of the opening. The barriers are incurvate, relative to the opening. The opening has a length across which junk cannot bridge. Consequently, the junk falls through the opening and is captured in an accumulator which underlies the opening. Knots substantially bridge across the opening, and impinge upon the arcuate barrier at the far end of the opening to be thrown upwardly for assimilation with the slurry flow coursing through the chamber. An elutriative liquid is supplied to the accumulator, at a given flow velocity, to wash up and out of the accumulator any organic particles which, due to irregularities, pass through the opening, to return the organic particles to the chamber.