If you own a printer and use it at all, you've likely learned that ink cartridges are annoyingly expensive. Cheap ones are expensive and expensive ones are obscene. Per gallon ink costs far more than gasoline or, better yet, Chanel No. 5 perfume.
Fear not avid printer, there is hope. If you haven't heard of it before, you can have the cartridge you already own simply refilled with ink instead of purchasing another cartridge. You may not have known about this, even if you've had your printer a long time -- you see, the big printer companies don't really want you to know about a cheap alternative to buying an expensive, swiftly diminishing product from them.
Refilling an ink cartridge is simple. I've refilled thousands. In just about every case, the ink cartridge has a sponge inside it, and vent holes on the cartridge. You simply fill the cartridge through the vent holes with a syringe and needle. That's it. You'll probably have to remove a sticker to reveal the vent holes. One can order a "refill kit" or the ink and syringes separate and refill the cartridge at home, or bring it to a local establishment that offers this service (Cartridge World, Walgreen's, and various other stores offer ink refilling). I definitely recommend the latter; refilling an ink cartridge can be very messy and they may be slightly clogged and need to be cleaned a certain way. Further, if it doesn't work for any reason, you should be able to get your money back rather than having wasted money if it doesn't work when you refill it. Furthermore, as newer designs of ink cartridges are being developed, this process is becoming more involved. The newest generations of ink cartridges are actually moving away from sponges, making refilling a cartridge a gauranteed mess.
When you try to use a refill cartridge to print, it will be slightly different. Because, as mentioned already, the major printer companies want you to buy from them they make using refills a bit of a hassle. The printer will display warning messages about voiding your printer warranty (there is legislation in place to prevent them from actually voiding the warranty over refills; they often say it "may" or "might" void your warranty) or that you're using a counterfeit cartridge (absurd; you had a genuine one refilled with the same ink). Many, many people confuse these warning for actual dangers in using refills, but that is simply not so. Also, the display that shows you how much ink is in each cartridge most likely won't read that the cartridge is full. This is less a ploy and more just a result of the software -- the printer doesn't actually measure how much ink is in the cartridge, the cartridge just has a page counter on it and after a certain number will always read empty. Thus, there is little reason to be concerned about not seeing the "ink level" of your cartridges. They aren't accurate and usually tell you're empty before you are, resulting in you buying more cartridges before you actually need to. You should always print until you see a drop in quality or missing spots, that's the biggest sign you are running out. On a daily basis I have customers bring me cartridges to refill that are still half-full or more and have never been refilled before because the printer told them the cartridge was out of ink.
If you are intent on refilling the cartridge yourself, you will need more information than this, like the specific type of ink and how much goes in the cartridge (overfilling them is bad news). I really don't recommend this, especially at home. Unless you've done it and are familiar its going to be a hassle, might not work, and could be very messy. Refills are generally very cheap, so you really can't be losing out on much by having it refilled by professionals. There is a certain, undeserved stigma around refilling ink cartridges, as if there is some danger in it. However, stigmas that make multi-million dollar tech companies millions more by keeping consumers scared and uninformed, by definition, shouldn't really be taken very seriously.