Abstract: A transparent housing for installation in a marine raw water line. The housing has an inlet chamber including a perforated plate disposed athwart the housing and comprising the downstream wall of the chamber. The plate permits water flow while acting to trap unwanted materials in the water stream. The transparent housing provides means for visual monitoring of the plate and of the interior of the inlet chamber. A sacrificial zinc pencil is disposed within the chamber to protect metal components and to provide a visual indication of the extent of electrolytic activity within the system. Debris in the sea water, for example, or from a broken pump impeller, or portions broken from the sacrificial anode, become trapped in the inlet chamber where they can be visually observed. In such cases, or when anode replacement is desired, the apparatus can be conveniently removed from service while appropriate changes are made.