Numerous factors played into the development of fountain pen filling systems. One among them was avoiding contact with the rim of the ink bottle, and the transference of ink to the fingers. That blot of ink on the thumb and index finger is not a good look.
The lever filler with, in most cases, the lever halfway along the barrel, seems to have been a major offender. The button filler was altogether better, keeping the hands well away from the bottle. The Leverless was similar in this respect. Of course all filling systems left the user with the necessity to wipe the nib once filled, with the risk of collecting some unwanted ink on the fingers.
The ultimate solution to the problem was that eccentricity, Sheaffer’s Snorkel, which completely isolated the fingers from the ink at all stages but at the cost of only containing a thimbleful of ink. This worked well for needle points and extra fines but any broader nib required many visits to the ink bottle.
Some fountain pen users don’t mind a little ink on the fingers, regarding it as a badge of honour. I hate it and I’m very careful around ink. I wear disposable nitrile gloves when I fill a pen and when stripping one down for repair. Some old inks redefine the word ‘permanent’ and have to wear off over time. Some others seem to have decayed over the decades since they were last used and smell absolutely dreadful.
I don’t have water on tap in my work area and I keep a container of water handy. I flush nib and section unit with a rubber bulb before removing the nib and feed. It is amazing how much ancient ink is stored therein. A good scrub with a brush and cotton buds restores the parts to a pristine condition.
It’s the nature of ink to permeate everything it touches and even ‘washable’ is only a relative term. There’s always the risk that a moment’s inattention can cause a horrible accident. That’s the price we pay for the pleasure of using fountain pens.