It is recommended to place the fountain pen without the cap with the nib pointing down in a glass and fill with lukewarm water (about 40 degrees) up to just below the turning knob. By the capillary action of the feed, the water is slowly drawn into the tank over several days; daily, the pen should be turned over once so that the water also reaches the piston. This method requires patience but usually succeeds. It is faster if the cone is unscrewed from the barrel with a special key and the barrel cleaned directly.