The invention relates to a dosing system comprising a dosing means for metering a liquid, especially an aqueous urea solution used for the after treatment of exhaust gases generated by combustion engines. The liquid can be conveyed from a reservoir into an exhaust manifold through the dosing means in a normally operating conveying device. According to the invention, at least one area that is located between a dosing point and the reservoir and is impinged upon by the liquid can be emptied counter to a normal transport direction of the liquid.