Extracorporeal blood circuit comprising: - a blood withdrawal line connectable to an inlet of a primary chamber of a filtration unit; - a blood return line connectable to an outlet of the primary chamber, the blood lines (6, 7) being configured for connection to a cardiovascular system of a patient; and - a container for fluids connected to the blood return line or to the blood withdrawal line, wherein the container is made from a substantially flexible material and comprises a bag having at least a first and a second film sealed to one another, the container comprises: • an inlet port configured for connecting to a fluid inlet line of a blood treatment apparatus; • an outlet port configured for connecting to a fluid outlet line of a blood treatment apparatus; and • a fluid conduit configured for putting the inlet port in fluid communication with the outlet port and comprising one or more deflection sections, wherein the fluid conduit has a non-constant width in a direction of fluid flow through the fluid conduit; - at least one of the one or more deflection sections further comprises an entry section and an exit section, each respective exit section being arranged downstream, in the direction of fluid flow, from each respective entry section; - the width (Lc) of the fluid conduit decreases along the direction of fluid flow through the entry section from a first width (L c) to a second width (L t) over a first distance (D e) and the width of the fluid conduit increases along the direction of fluid flow through the exit section over a second distance (D x), the first distance and the second distance being different from one another. - a blood withdrawal line connectable to an inlet of a primary chamber of a filtration unit; - a blood return line connectable to an outlet of the primary chamber, the blood lines (6, 7) being configured for connection to a cardiovascular system of a patient; and - a container for fluids connected to the blood return line or to the blood withdrawal line, wherein the container is made from a substantially flexible material and comprises a bag having at least a first and a second film sealed to one another, the container comprises: • an inlet port configured for connecting to a fluid inlet line of a blood treatment apparatus; • an outlet port configured for connecting to a fluid outlet line of a blood treatment apparatus; and • a fluid conduit configured for putting the inlet port in fluid communication with the outlet port and comprising one or more deflection sections, wherein the fluid conduit has a non-constant width in a direction of fluid flow through the fluid conduit; - at least one of the one or more deflection sections further comprises an entry section and an exit section, each respective exit section being arranged downstream, in the direction of fluid flow, from each respective entry section; - the width (Lc) of the fluid conduit decreases along the direction of fluid flow through the entry section from a first width (L c) to a second width (L t) over a first distance (D e) and the width of the fluid conduit increases along the direction of fluid flow through the exit section over a second distance (D x), the first distance and the second distance being different from one another. • an inlet port configured for connecting to a fluid inlet line of a blood treatment apparatus; • an outlet port configured for connecting to a fluid outlet line of a blood treatment apparatus; and • a fluid conduit configured for putting the inlet port in fluid communication with the outlet port and comprising one or more deflection sections, wherein the fluid conduit has a non-constant width in a direction of fluid flow through the fluid conduit; - at least one of the one or more deflection sections further comprises an entry section and an exit section, each respective exit section being arranged downstream, in the direction of fluid flow, from each respective entry section; - the width (Lc) of the fluid conduit decreases along the direction of fluid flow through the entry section from a first width (L c) to a second width (L t) over a first distance (D e) and the width of the fluid conduit increases along the direction of fluid flow through the exit section over a second distance (D x), the first distance and the second distance being different from one another. - at least one of the one or more deflection sections further comprises an entry section and an exit section, each respective exit section being arranged downstream, in the direction of fluid flow, from each respective entry section; - the width (Lc) of the fluid conduit decreases along the direction of fluid flow through the entry section from a first width (L c) to a second width (L t) over a first distance (D e) and the width of the fluid conduit increases along the direction of fluid flow through the exit section over a second distance (D x), the first distance and the second distance being different from one another.