Abstract: The visual monitoring apparatus includes a transparent tube section with coupling flanges at each end for coupling to adjacent conduit sections carrying a stream of conditioned sludge which includes agglomerated solid bodies. Control rods extend between the coupling flanges to strengthen the tube. A strobe light is mounted in a housing which is mountable alongside the tube and closely conforms to the shape thereof for confining the strobe light to a predetermined area of the tube and isolating that area from ambient light. The housing accommodates the control rods therethrough and contains a mirror which directs light reflected from the illuminated contents of the tube along a viewing path through a view port in the housing which is closed by a door or hatch. The frequency of the strobe can be adjusted to correspond to the flow rate of the fluid in the tube for creating the visual impression of substantially stopping the movement of the solid bodies in the tube.