I should probably know this after years of owning, collection and using pre 1930 Waterman pens.
I just replaced the rubber sac on one of my pens and was wondering if there is an ideal length of the sac in relation to the lever box?

I tend to leave about an inch or so beyond the back of the lever box.
It seems that if the sac is much longer than the lever box, the area behind the box would not get totally cleaned out. But the longer sac would hold more ink.
But I'm really not sure.