A model for the dynamic behaviour of wet front distance and liquid saturation in rectangular capillary suction apparatus (RCSA) is developed. Governing equations based on the mass/momentum balance are derived and solved numerically. The calculation shows that the effects of the initial conditions on system dynamics vanish rapidly, and the system will then evolve along a slow manifold independent of the initial conditions. When time is large, the dimensionless wet front distance with time is a straight line on a log-log plot with slope 1/2, and the liquid saturation under the inner cell will approach to a constant which depends only on the product of solid concentration and the averaged specific resistance if the RCSA is fixed. Optimum experimental conditions are suggested. A rapid method based on the model for estimating the averaged specific resistance of cake is proposed and compared with experimental findings.