Provided is an improved filtration module assembly comprising a vessel having a filtration cartridge disposed within it and a header coupled to an end of the vessel, the header including a housing having an open-ended upper end and a lower end, and an end cap including a portion that mates with a complimentary structure defined by the inner wall of the open ended upper end of the housing to removably engage with the housing and the end cap may further define a passageway for fluid to flow out of the vessel. The filtration module assembly may enable an improved manifold arrangement used to communicate fluids to and from a filtration system comprising a plurality of such modules and the configurations of the present invention may facilitate improved operation of such filtration systems.