Abstract: A horizontal circular filter is provided which includes plural filter pans arranged in a circle and rotatable as a group around a fixed central vacuum box. The filter pans are connected to respective sections of the vacuum box by respective manifolds which rotate with the filter pans. Each of the filter pans comprises a pan having a flat bottom wall including plural filtrate drainage troughs therein. A removable, disposable, plastic channel-forming grid is positioned on the bottom wall between the side walls of the pan. A filter cloth is disposed over the grid, and a cloth "caulking" arrangement secures the filter cloth in place so as to also hold the grid in place in the pan. A method of retrofitting existing punched plate filter pans is also provided.