Abstract: A structure for use with water drainage inlets includes an outside wall portion, a perforated bottom portion, and an inside wall portion. The outside wall, bottom, and inside wall together define a trough for retention of a replaceable filter media. The trough is installed on the inside surface of a drainage structure so that drainage water that would normally flow directly through the drainage structure is caused instead to flow through the filter media, thereby removing undesirable materials that may be carried in the water, while permitting the water itself to pass through essentially unimpeded to the ultimate drainage location.