Rolled-up paper towel strip inside Diplomat converter

The opening on a Diplomat ‘international standard’ converter is 2.4mm across, and other ‘non-conformant’ types of converters tend to have wider openings than that. Even a completely dry and still relatively stiff strip of paper towel can be rolled up to be inserted through the opening; and, once its slightly moist and softer, it can easily deform and bunch up to touch (and therefore dry) the walls of the converter as the strip is rotated.

I keep a stack of these strips handy for cleaning.