A process for preparing a bulk multi-metallic catalyst for hydrotreating heavy oil feeds is provided. An optical probe is positioned within the manifold body to receive light from a light source, preferably an optical fiber, and to illuminate the waterfall by optical transmission through the outlet body. The example torque transducer is fabricated from a steel alloy including between 17 and 35% chromium, 5 to 20% cobalt and the remainder iron. A rod 14 formed with a rack 14A extends from the second piston 72.