The invention concerns a manifold comprising: an auxiliary block (3) having cassette feed ports (20) and cassette filtrate return ports (21) each emerging through a bearing surface (7) and, on a counter-bearing surface (8) situated on the opposite side to the bearing surface (7), first recesses into each of which emerges a cassette filtrate return port (21); a main block (2) on which is fastened the auxiliary block (3), having an inlet conduit (14) and a filtrate outlet conduit (15), cassette feed intermediate ports which communicate with the inlet conduit (14) and with a cassette feed port (20), conveying cut-outs each facing a recess, and cassette filtrate return intermediate ports which communicate with the filtrate outlet conduit (15) and with a cassette filtrate return port (21).