Montblanc recommends cleaning fountain pens at least once a month with clear water; with black ink more often. Simply holding the 147 under water is, however, problematic because the inner metal parts can oxidise; only by long drying before renewed use can this danger be reduced, although ink residues can hardly be removed completely this way. An ultrasonic bath is another possibility, but rarely available in practice; in addition, a simple ink change is hardly possible with it. The most practical approach is to fit a standard Montblanc piston converter, which fits well and protrudes far enough out of the barrel to be operated comfortably; with it, cleaning the 147 becomes an easy routine.
Related pages on fountainpen.de:
• Montblanc Meisterstück 147 Traveller: https://www.fountainpen.de/c-montblanc-meisterstueck-147-en.htm