A survey tool for attachment to a drill string for inserting the survey tool into a borehole, the survey tool comprising a housing having a proximal end adapted for attachment to the drill string and a bore traversing the housing adapted to receive fluid from the drill string, and a piston adapted to be received within the bore, the piston being adapted to be selectively displaced between at least a first condition and a second condition, wherein in the first condition the fluid exists the housing at a first location and in the second condition the fluid exists the housing at a second location.