By providing a lubricating system with a strategically positioned sight-glass, it is possible to replace an fuel filter without either spilling large amounts of fuel all over or allowing for air bubbles, which can degrade the lubricating system's operation and cause siphoning. The sight-glass is positioned below the fuel inlet and outlet passages but below the filter. Thus, as soon as no fuel is seen in the sight-glass, a mechanic knows that the fuel filter has been substantially emptied of fuel yet the fuel inlet and outlet are still full.