Piping system for chemical liquids, in particular oil products, such as fuels, at least comprising a double-walled plastic conveyor pipe (3) with an inlet and an outlet, the double-walled pipe (3) comprising, in the double wall, one or more intermediate spaces extending along the length of the pipe (3), in which the piping system furthermore comprises gas-conveying means which comprise a gas-suction device which is connected to the intermediate spaces in such a manner that, in operation, gas can be sucked through the intermediate spaces. A piping system of this nature is suitable in particular for underground use at a petrol station.