The Bother of Breather Tubes

They’re not much of a bother actually, unless you lose it. In fact,
they’re quite helpful. Piston-fillers and pump fillers often don’t fill
completely because the air gets stuck and cannot be expelled
without expelling ink. Breather tubes allow a pen to hold more ink
because the tube lets the air that’s stuck at the end of the
reservoir to be expelled instead of the ink that’s already in the
reservoir. The Parker Vacumatic can be filled by pumping the filler
through a few cycles.