We consider a deformable multiphase multicomponent porous medium submitted to gradients of hydraulic and electric potentials. The physical balance laws are written using principles of mechanics of continuous and porous media and the liquid phase transport relation is developed using linear thermodynamics of irreversible processes. An experimental validation of this transport relation is proposed in the case of agar gel, which is a biphasic biopolymer. An electro-osmotic cell is developed and we show that there is a good superposition of the two thermodynamic forces