The initial stage of compact formation from a suspension in a cylindrical cell is studied analytically using a variable resistance and a diffusion-type term in the constitutive equation. The resistance is dependent on the amount of material that has settled on the septum; it is treated as a phenomenological variable. The diffusion term is proportional to the gradient in the solidosity. Experimental verification of the predictions of the theory show excellent agreement up to second order in the pressure. zeta-polential and density dependence of the resistance of the clogged septum are also determined.