Knowing how to refill your used Hewlett-Packard (HP) ink cartridges can save you a lot of money depending on how much you use your printer. Simply keep your original ink cartridges and refill them whenever ink runs out. Your only cost is buying an ink refill kit and ink whenever necessary.

Refilling an Ink Cartridge

Purchase an ink refill kit and a few bottles of ink so you will not have to run back to the store every time you run out of ink. Put the ink cartridge on a paper towel or something thicker, such as cardboard, that will absorb any spills. Fill the syringe, which is provided with the refill kit, with enough ink as your printer's sponge can hold. A good rule of thumb is to fill the syringe with half the ink that would fill the ink cartridge if there was no sponge. If your filling hole is closed, read the manufacturer's instructions on how to open it. Push the needle of the syringe into the ink cartridge sponge and slowly force the ink into the sponge. Do not use a lot of pressure, which could overwhelm the sponge and possibly ruin your ink cartridge, making ink flow out unevenly. Fill the ink cartridge until the sponge looks moist. Do not fill the cartridge so full that the ink might spill if the cartridge tips over. Now clean up the filling hole with a paper towel until there are no ink smears remaining. Close your cartridge's filling hole if necessary according to the manufacturer's instructions; tilt it around a few times to confirm how much liquid is moving around in the cartridge. If there's excess ink, open the cartridge and spill out the excess. It is always better to fill the cartridge short of maximum volume. Now you can pop the ink cartridge into the printer and test it out a few times by running "head cleaning." Print out a page just to make sure it works.

Source:

HP Refilling Manual (comes with every HP printer)