The present invention relates to a device for manually metering liquids, for example a pipette or a metering button. The device comprises a joint forming a seal between a hollow cylinder and a piston housed inside the cylinder, the piston being moved vertically so as to suck in or expel the liquid. During the metering operation, the joint remains fixed with respect to the movement of the piston and comprises parts formed by portions having dedicated geometric and mechanical characteristics which make it possible to locally optimize the functions of sliding, sealing and fastening in the cylinder.