Abstract: Porous, tubular core sections coated with a semipermeable membrane are joined at their ends by a simplified coupling member. Each coupling member or connector comprises a cylindrical flange member having helically ribbed or barbed nipples which fit tightly into the ends of bores of adjacent core sections. The ends of the cores abut against the circular part of the coupling member. The ribs on the nipples on the coupling member are resilient and deform when inserted. The nipples have neck parts of a smaller diameter adjacent the body part of the coupling member providing annular spaces between these neck parts and the bores of core members permitting continuous flow of permeate and cleaning solution into these spaces and helically along the nipples. There are no appendages, cavities or pockets in which permeate or cleaning solution could be trapped.