A liquid-impervious tube, includes at least one first band helically wound on itself, characterized in that this first band is porous and pervious to gaseous fluids and in that it includes a second thin band which is pervious to gaseous fluids and impervious to liquids, and which is also helically wound on itself, with partial overlapping of its turns, said turns being secured to one another in a impervious manner so that the second band defines a liquid-impervious continuous covering.