Flow across a semi-permeable membrane

Hi ,

I am trying to model flow through a semi-permeable membrane due to a pressure gradient. For now, I am using free and porous media flow physics and for my geometry, I have set up 3 rectangles next to each other. The middle rectangle has been designated to be the porous material, and the rectangles on the ends are the fluid materials.
Am I approaching this problem correctly with COMSOL? If not, what is the best way to approach this? How am I suppose to specify 2 separate pressures on both sides of the membrane to drive fluid flow across the membrane?

Thank you so much,
Aaron