The fountain pen is filled and emptied several times with clear water; usually this is sufficient in less than a minute, until the water remains clear. With stubborn residues, one can place the pen overnight nib-down in a glass of water or shake it vigorously with water plus a little air, in order to loosen ink from the tank. Then push out residual water with the piston and dry the nib with a cloth. As a last resort, an ultrasonic bath with distilled water helps, into which, however, only the nib and at most 0.5 cm of the barrel should be immersed.