An endcap comprising: a ring shaped first wall including a plate shape perpendicular to a longitudinal axis, a radial inner portion and a radial outer portion; a cylindrical flange disposed between the radial inner portion and the radial outer portion and projecting axially along the longitudinal axis in a first direction; an inner cylindrically shaped wall projecting axially along the longitudinal axis opposite the first direction from the radial inner portion of the first wall; a cylindrically shaped wall extending along longitudinal axis in said first direction, disposed radially outward from the radial outer portion of the first wall and connected to the first wall by a plurality of arms, wherein the cylindrically shaped wall, the plurality of arms, and the first wall cooperate to define a plurality of apertures; a ring shaped wall disposed radially outward from the cylindrically shaped wall in a direction perpendicular to said longitudinal axis; an outer seal member disposed adjacent the radially outermost edge of the ring shaped wall; said endcap being characterised in that it comprises an inner seal member integrally connected to the cylindrical flange, the inner seal member including a first portion engaged with an inwardly radially facing surface of the cylindrical flange; and in that it comprises an anti-prefill device configured to reduce and/or prevent the flow through an opening in the first wall defined by the radial inner portion during priming, wherein the anti-prefill device includes a cap portion axially spaced from the first wall in the first direction and covering the opening in the first wall defined by the radial inner portion, a plurality of wall portions attaching the cap portion to the first wall, the plurality of wall portions establishing a radially facing wall including apertures, and a cylindrical wall disposed radially within the plurality of wall portions, the cylindrical wall being attached to the first wall to surround the opening in the first wall defined by the radial inner portion and projects axially along the longitudinal axis in the first direction over a greater distance than the distance that flange axially projects from first wall, the free end of the cylindrical wall being axially spaced from the cap portion. a ring shaped first wall including a plate shape perpendicular to a longitudinal axis, a radial inner portion and a radial outer portion; a cylindrical flange disposed between the radial inner portion and the radial outer portion and projecting axially along the longitudinal axis in a first direction; an inner cylindrically shaped wall projecting axially along the longitudinal axis opposite the first direction from the radial inner portion of the first wall; a cylindrically shaped wall extending along longitudinal axis in said first direction, disposed radially outward from the radial outer portion of the first wall and connected to the first wall by a plurality of arms, wherein the cylindrically shaped wall, the plurality of arms, and the first wall cooperate to define a plurality of apertures; a ring shaped wall disposed radially outward from the cylindrically shaped wall in a direction perpendicular to said longitudinal axis; an outer seal member disposed adjacent the radially outermost edge of the ring shaped wall; said endcap being characterised in that it comprises an inner seal member integrally connected to the cylindrical flange, the inner seal member including a first portion engaged with an inwardly radially facing surface of the cylindrical flange; and in that it comprises an anti-prefill device configured to reduce and/or prevent the flow through an opening in the first wall defined by the radial inner portion during priming, wherein the anti-prefill device includes a cap portion axially spaced from the first wall in the first direction and covering the opening in the first wall defined by the radial inner portion, a plurality of wall portions attaching the cap portion to the first wall, the plurality of wall portions establishing a radially facing wall including apertures, and a cylindrical wall disposed radially within the plurality of wall portions, the cylindrical wall being attached to the first wall to surround the opening in the first wall defined by the radial inner portion and projects axially along the longitudinal axis in the first direction over a greater distance than the distance that flange axially projects from first wall, the free end of the cylindrical wall being axially spaced from the cap portion.