Mercury - Waste Level Gauge Black Face 2-1/8" (52 mm) 79-8M0052847. Overview. The Mercury Waste Level Gauge (79-8M0052847) keeps you informed of your holding tank levels so you can plan pump-outs before they're needed. It features a black face, clean white markings, and a glass lens for crisp, easy visibility in any lighting. Built to fit a standard 2-1/8" (52 mm) dash hole, this gauge integrates with SmartCraft systems when compatible sensors are installed. It's durable, easy to read, and desig