Method and device for metering a medium from at least one storage tank by a metering device, which has a piston pump, which defines a working chamber with a cylinder and a piston, wherein in a first method step a determined filling quantity of a medium is conveyed via an inlet valve into the working chamber and the determined filling quantity is greater than the quantity to be metered and, in a second method step, the piston reduces the working chamber in size enough that only the quantity to be metered remains, wherein the excess medium flows out of the working chamber, wherein the excess medium flows via the inlet valve back into a ring line, which is connected in a medium-conducting manner to the storage tank and is arranged outside the working chamber.