Summary: When refilling an HP 94 ink cartridge, first remove the sticker that has been placed on it by the manufacturer. Avoid overfilling the HP 94 ink cartridge with help from an employee of an ink-filling station in this free video on HP printer cartridges.
"Hi this is Taylor. We are here talking about HP cartridges. Today we are going to discuss how to refill an HP 94 cartridge. HP 94 cartridges are fairly simple to refill. The manufacturers placed a label, which you need to remove. Once you remove that, you only need to remove so much, and then poke through, or hopefully it does not rip, and it will expose a hole up top. There is also another one here and over here. Unnecessary to uncover if you are refilling. Once you have uncovered it, all you need to do is get a needle and your HP ink, fill up the syringe, and insert twenty milliliters. Once you have filled it up, I do recommend giving a quick cleaning with a bath of hot water, and then completely drain the cartridge before you insert it back into the machine."
eHow Article: How to Refill HP 94 Ink Cartridges