Refilling an ink cartridge is accomplished using a syringe with the right amount of ink and filling the proper chamber with the ink. Depending on the color and type of cartridge, there are variations on how to do this.
Before refilling, it is important to check the appropriate process for the specific cartridge. For the Dell #J740, for example, the black cartridge is refilled by drilling a small hole on top of the cartridge, using a 1/16-inch thumb drill, and emptying a syringe filled with 25 cubic centimeters of black ink into the ink chamber. The color #j7240 has holes on top of the chambers already, but a cap covering them needs to be removed before injecting 8 milliliters of ink into the proper chambers.