A drag force approach to the transport of colloids in unsaturated soils is introduced. It is based on film flow which is due to momentum dissipation during porous media flow. Supporting results are from three types of colloid transport experiments: (1) sprinkling of a latex bead and methylene blue suspension in situ on the surface of a forest soil with subsequent bead collection underneath, (2) application of bead suspension to a column of undisturbed soil and purging of retained beads, and (3) application of a suspension with 5 bacteriophages to a different soil column. Relative colloid breakthrough concentrations in relation to the drag forces, P/P0, versus Fd(t)/A, were well pronounced during bead breakthrough, and bead diameters had no significant impact. In contrast, phage breakthrough showed a wide range of behavior. Previous bacteria breakthrough experiments support the approach; however, site-specific soil properties should also be considered.