The behavior of surfactant solutions through a porous medium is solely due to shear. Despite pronounced rheopexy, one rheological property that can uniquely be correlated with porous medium flow data is the shear stress tau. A correlation of the same type allows us to account for the effects of variable viscosity in the case of polymeric solutions. The onset of increased resistance, which remains after this viscosity correction, occurs at the very same stress tau, at which the first normal stress difference N-1 equals tau in viscometric flows. This stress tau is a universal constant, characteristic of the type of polymer solution. From these results it follows (a) that the Deborah number concept emerges in the c --> 0 limit (infinitely dilute solution), (b) that outside this limit (finite c) the Deborah number concept cannot be applied and (c) that the non-viscous behavior in porous medium flow is a normal stress effect, i.e. it is elastic in origin. It can also be described by the concept of shear waves. The onset criterion, N-1/tau approximate to 1, allows upscaling.