only one direction in many embodiments the manifold 11 may include first and second permeate collection passages 14 a 14 b that are isolated from one another as shown in fig3 and 4 the first and second permeate collection passages 14 a 14 b may collect permeate from different isolated sources for example as shown in fig1 the first and second permeate collection passages 14 a 14 b may collect permeate from first and second sets 12 a 12 b of filtration units 13 respectively and may be isolated from the permeate which passes through the filtration media of the second and first sets 12 b 12 a of filtration units 13 respectively the first and second permeate passages 14 a 14 b are isolated from each other and are not in fluid communication at any point inside the manifold isolation of the first permeate from the second permeate inside the manifold or inside the filtration assembly may not exclude the combination of the first and second permeates on the exterior of the manifold or the exterior of the filtration assembly for example following filtration and or sampling in some embodiments the first collection passage 14 a may collect permeate from filtration units 13 of the first filter set 12 a e g on the first side 16 a of the body 15 of the manifold 11 but may be fluidly isolated from filtration units 13 of the second filter set 12 b e g on the second side 16 b of the body 15 of the bidirectional manifold 11 the second permeate collection passage 14 b may collect.