One larger [1] and one smaller tube [2], forming a functional unit with the smaller tube [2] positioned within the larger tube [1], both tubes are relocatable and demountable, both tubes with an aperture [3 and 4] at both ends, at least one aperture [5] being provided in the wall of the outer tube located at a distance of about between 1 mm and 10 cm from the tip [6], or several apertures positioned in a segment of 1-250 mm from the tip, wherein the diameter of the single aperture is between 70% and 120% of the inner diameter of the outer tube [1], or in case of several apertures, for each aperture 30-60% of the inner diameter of the outer tube, wherein the outer diameter of the inner tube is between 0.6 mm and 2.0 mm (F2 to F6), the outer diameter of the outer tube is between 1.3 mm and 3.6 mm (F4 to F11), and the distance between the outer wall of the inner tube and the inner wall of the outer tube is between 0.1 mm to 3.0 mm.
