So because of this, I would go out and buy new ones because I didn't know any better. Well come to find out, the cartridges weren't empty. The printheads were just dried up and clogged so I wasn't getting good prints. I was thrilled when I learned this trick, because it's saved me so much money already and I don't have to waste perfectly good cartridges that still have some life left in them.
Soak the HP cartridge in a little boiling water for 15 minutes.
All one does is boil some water and place the ink cartridge, printer head down, into a container filled with just enough water to cover the head for about 15 minutes. That's it! The inks are water soluble so the hot stream will loosen the dry ink on the head and the cartridge is as good as new. Try it next time you notice that your prints are not coming out as good as normal. It might just be a clogged cartridge.