Probably the hardest cartridge to refill is the HP C6578. If you've mastered this one give yourself a hardy pat on the back. HP color cartridges like the C1823, the forbearer to the C6578, have been a challenge to refillers because of the unique design that I'm sure was carefully engineered to thwart refilling.
Conversely and ironically, HP couples this with a black cartridge that is a snap to refill, the 51645A and C6615. Go figure. But we still didn't get to the easiest one to refill. Keep reading.
Lexmark cartridges have followed the same basic designs as HP. You can see a remarkable resemblance in the Lexmark 12A1980 and its
counterpart 15M0120 to HP's 51625A and 51649A color cartridges. All of these cartridges are a pain to refill but can be done with great success if you know the secret, and that is to remove the sponges and clean them with warm water before refilling.
Lexmark's 10N0016, 10N0026, 18L0032 and 18L0042 are remarkably similar to HP's C6656, C6657, C8727 and C8728. Not surprisingly they
refill the same way and the results are mixed. Occasionally I'll receive an email from somebody having problems refilling these cartridges
but it usually is because they are refilling to fast or something like that.
Moving along with our analysis, the next in terms of difficulty, or ease, depending on how you want to read this article, is Epson. Epson's are generally not that hard to refill but still there are tricks that will help you succeed. The biggest problem I see with Epson cartridges, aside from the chips, is it's easy to inject air which causes micro bubbles which results in spotty printing. Advanced Epson refillers know to extract the foamy air from an Epson cartridge before refilling it.
Last but not least is the easiest cartridge in the world to refill. Have you guessed yet? Repeat after me.... CANON BCI-3e and BCI-6. Canon does not use any technology on these cartridges which immediately gives them a leg up over Epson. These two cartridges are identical in physical form so from now on I will address them in the singular. The only problem with refilling this cartridge (actually more accurately a ink tank) is that if you don't get a good airtight seal over the refill hole it WILL leak. The best thing you can use is a hot glue gun. It seals the hole very well and the bubble of glue is easily removed with your fingernail when It's ready for the next refill. We can't put a hot glue gun in a refill kit so the next best thing is a 4 x 3/8 stainless steel screw if you use a 1/16" drill bit to make the refill hole.