Both the Conid Bulkfiller and the PenBBS 355 fountain pens are piston or syringe fillers with a great technical advancement. After pulling back on the piston, the rod can be disengaged from the piston head and then put back down into the barrel without moving the piston. This results in the piston moving much farther along the barrel that possible with most other filling systems. Paul E. Wirt made a pen with a similar filling system 100+ years prior. It was a bit less elegant and not as easy to tell if the rod has engaged the piston.
Here is a video of the PenBBS version.