A device for transferring a fluid from a surgical site, comprising: an elongate body portion defining a proximal end region connectable to a source of negative pressure; an elongate neck portion defining a distal end region of the device locatable at a surgical site; a through bore extending from the distal end region to the proximal end region; a control member for selectively controlling a negative pressure at the distal end region, wherein the control member is slidably mounted in an aperture of the body portion to allow the same to move inwardly and outwardly with respect to the body portion and comprises a valve portion extending downwardly from a button portion, wherein the valve portion is moveable across the through bore from an open position towards a closed position to at least partially restrict a fluid flowing along the through bore; and a biasing element to urge the valve portion towards the open position when no force is being applied to the button portion, characterised in that the button portion comprises at least one upper projection extending outwardly from a proximal and upper end region of the button portion for engagement with a lip region extending inwardly from an upper edge region of the aperture, wherein, when the button portion is depressed, the upper projection is engageable with an upper surface of the lip region to limit said inward movement of the control member with respect to the body portion and in turn the valve portion when in the closed position, and wherein, when the button portion is further depressed to urge the upper projection past and under the lip region, the upper projection is engageable with a lower surface of the lip region to constrain the control member against a reaction force of the biasing element and prevent the valve portion returning to the open position when no force is being applied to the button portion to thereby lock the valve portion in the closed position, and wherein the control member is configured to tilt or move forwardly in a distal-proximal direction within the aperture to allow the upper projection of the button portion to clear the lip region and allow the control member to be urged outwardly with respect to the body portion, and in turn the valve portion towards the open position, by the biasing element. an elongate body portion defining a proximal end region connectable to a source of negative pressure; an elongate neck portion defining a distal end region of the device locatable at a surgical site; a through bore extending from the distal end region to the proximal end region; a control member for selectively controlling a negative pressure at the distal end region, wherein the control member is slidably mounted in an aperture of the body portion to allow the same to move inwardly and outwardly with respect to the body portion and comprises a valve portion extending downwardly from a button portion, wherein the valve portion is moveable across the through bore from an open position towards a closed position to at least partially restrict a fluid flowing along the through bore; and a biasing element to urge the valve portion towards the open position when no force is being applied to the button portion, characterised in that the button portion comprises at least one upper projection extending outwardly from a proximal and upper end region of the button portion for engagement with a lip region extending inwardly from an upper edge region of the aperture, wherein, when the button portion is depressed, the upper projection is engageable with an upper surface of the lip region to limit said inward movement of the control member with respect to the body portion and in turn the valve portion when in the closed position, and wherein, when the button portion is further depressed to urge the upper projection past and under the lip region, the upper projection is engageable with a lower surface of the lip region to constrain the control member against a reaction force of the biasing element and prevent the valve portion returning to the open position when no force is being applied to the button portion to thereby lock the valve portion in the closed position, and wherein the control member is configured to tilt or move forwardly in a distal-proximal direction within the aperture to allow the upper projection of the button portion to clear the lip region and allow the control member to be urged outwardly with respect to the body portion, and in turn the valve portion towards the open position, by the biasing element.