The paper outlines the lessons learned from a series of stress testing and optimization studies performed at several municipal wastewater treatment plants in the Pacific Northwest. Installations tested included gravity belt and dissolved air flotation thickeners, and belt filter presses. In some cases, significant gains in rated capacity were achieved through stress testing, while process optimization addressed such variables as polymer dose, feed composition, flight operation, and belt speed, tension, and material. This paper outlines a general approach to solids systems stress testing, with details from each case study and discussion of test results.