A flow control element for controlling the flow of a liquid comprising: a wall section surrounding a liquid flow channel; and a substantially flat elastic membrane connected to the wall section and extending across the liquid flow channel, wherein the elastic membrane defines a plurality of first pinholes and a plurality of second pinholes, wherein said pluralities of first pinholes and second pinholes are formed such that: when the membrane is subjected to normal atmospheric conditions, both the first pinholes and the second pinholes remain closed to prevent liquid flow from the liquid flow channel through the membrane, when the membrane is subjected to a first, relatively low applied pressure differential, the first pinholes remain closed and the second pinholes open to facilitate a first, relatively low liquid flow rate through the membrane, and when the membrane is subjected to a second, relatively high applied pressure differential, both the first pinholes and the second pinholes open to facilitate a second, relatively high liquid flow rate through the membrane; characterised in that the plurality of second pinholes are formed using a larger pin than that used to form the plurality of first pinholes so that the elastic closing force that pinches the closed first pinholes is larger than the elastic closing force pinching the closed second pinholes. a wall section surrounding a liquid flow channel; and a substantially flat elastic membrane connected to the wall section and extending across the liquid flow channel, wherein the elastic membrane defines a plurality of first pinholes and a plurality of second pinholes, wherein said pluralities of first pinholes and second pinholes are formed such that: when the membrane is subjected to normal atmospheric conditions, both the first pinholes and the second pinholes remain closed to prevent liquid flow from the liquid flow channel through the membrane, when the membrane is subjected to a first, relatively low applied pressure differential, the first pinholes remain closed and the second pinholes open to facilitate a first, relatively low liquid flow rate through the membrane, and when the membrane is subjected to a second, relatively high applied pressure differential, both the first pinholes and the second pinholes open to facilitate a second, relatively high liquid flow rate through the membrane; characterised in that the plurality of second pinholes are formed using a larger pin than that used to form the plurality of first pinholes so that the elastic closing force that pinches the closed first pinholes is larger than the elastic closing force pinching the closed second pinholes. when the membrane is subjected to normal atmospheric conditions, both the first pinholes and the second pinholes remain closed to prevent liquid flow from the liquid flow channel through the membrane, when the membrane is subjected to a first, relatively low applied pressure differential, the first pinholes remain closed and the second pinholes open to facilitate a first, relatively low liquid flow rate through the membrane, and when the membrane is subjected to a second, relatively high applied pressure differential, both the first pinholes and the second pinholes open to facilitate a second, relatively high liquid flow rate through the membrane; characterised in that the plurality of second pinholes are formed using a larger pin than that used to form the plurality of first pinholes so that the elastic closing force that pinches the closed first pinholes is larger than the elastic closing force pinching the closed second pinholes.