The capillary suction time (CST) apparatus has been studied both theoretically and experimentally. First, a theoretical model is presented for the description of the liquid flow in a capillary suction time apparatus. Second, to obtain reliable reproducible experimental data, a new CST apparatus has been developed. The filter paper, used as a capillary medium in the conventional CST apparatus, is replaced by ceramics, and the position of the liquid front is determined continuously by measuring the electrical resistance of (the wetted) ceramics as a function of time. As a consequence the theoretical model can be checked far better with the experimental results than with the conventional CST apparatus, which determines the position of the liquid front at only two fixed positions. Specific cake resistances can be determined by use of the presented model and the new equipment, using the right properties (permeability and porosity) and dimensions of the ceramic slab (thickness). The dewatering behavior of unflocculated and flocculated sludge and the effect of slurry concentrations can be investigated.