Abstract: A sight glass and sampling system for the output of a liquid processing device. The system includes a sight glass connected to the outlet of a liquid processing device. A first three-way valve controls the flow from the outlet of the liquid processing device to the inlet of the sight glass. A second three-way valve controls the outlet from the sight glass. A valve controlled sample conduit is connected between the first and second three-way valves. A bypass conduit connects the first and second three-way valves and is controlled by these valves.