A mathematical model termed the blind side channel model is developed to describe the washing performance of liquid retained in a bed of granular solids. The effects of operating variables and system's parameters, such as the flow rate of wash liquor, the diffusivity of the liquid system, and the thickness of the bed, are discussed. The experimental washing study was carried out with granular solids such as glass beads, sand, and crystalline solids, and application of wash liquors miscible in all cases with the residual liquid in the bed, drained by centrifuging. Results from the developed model showed very good agreement with the experimental results. The developed model would be valuable in analyzing the washing performance for process improvement and in designing washing systems.