A method of introducing liquid into a gap of a digital microfluidics system for manipulating samples in liquid portions or droplets; the digital microfluidics system comprising a first substrate and a central control unit, wherein said first substrate comprises an array of electrodes, and wherein said central control unit is in operative connection to said electrodes for controlling the selection of individual electrodes thereof and for providing a number of said electrodes with voltage for manipulating liquid portions or droplets by electrowetting; in said digital microfluidics system, a working gap with a gap height is located parallel to the array of electrodes and in-between first and second hydrophobic surfaces (26,28); the two hydrophobic surfaces (26,28) facing each other at least during operation of the digital microfluidics system, characterized in that the method comprises the steps of: (a) placing a cover on the first substrate of the digital microfluidics system, the cover comprising on one side the second hydrophobic surface and on another side at least one micro-container interface; said at least one micro-container interface comprising a cone with an inner surface and at least one fluidic access hole formed into the cover and interconnecting the cone and the gap; (b) providing an essentially uniform height of the gap between said first and second hydrophobic surfaces (26,28); (c) providing at least one micro-container filled with prepackaged liquid reagents; (d) inserting a nozzle of the at least one micro-container into the cone of the micro-container interface of the cover; (e) creating a sealing form fit contact between the inner surface of the cone of the micro-container interface and an outer surface of the nozzle of the inserted at least one micro-container; and (f) dispensing liquid by positive displacement from the at least one micro-container into the gap via the at least one fluidic access hole formed in the cover, wherein the injection of liquid into the gap occurs by positive displacement when a piston of the micro-container is pushed down by a mechanical actuation. (a) placing a cover on the first substrate of the digital microfluidics system, the cover comprising on one side the second hydrophobic surface and on another side at least one micro-container interface; said at least one micro-container interface comprising a cone with an inner surface and at least one fluidic access hole formed into the cover and interconnecting the cone and the gap; (b) providing an essentially uniform height of the gap between said first and second hydrophobic surfaces (26,28); (c) providing at least one micro-container filled with prepackaged liquid reagents; (d) inserting a nozzle of the at least one micro-container into the cone of the micro-container interface of the cover; (e) creating a sealing form fit contact between the inner surface of the cone of the micro-container interface and an outer surface of the nozzle of the inserted at least one micro-container; and (f) dispensing liquid by positive displacement from the at least one micro-container into the gap via the at least one fluidic access hole formed in the cover, wherein the injection of liquid into the gap occurs by positive displacement when a piston of the micro-container is pushed down by a mechanical actuation.