Late model Epson (desktop printer) ink cartridges are not refillable. Not only is it difficult to physically fill them, but because it's not possible to reset the cartridge chips or disable the ink monitoring, it's largely a waste of time. Fitting a refilled cartridge will return "Ink cartridge can not be recognised" printer error and there is absolutely nothing you can do to make the printer work - other than fitting new cartridge(s).
But that doesn't mean you have to give up on ink refilling and keep buying new Epson cartridges. It simply means that you'll need a set of refillable cartridges - as well as the refill ink. Once you have refillable cartridges, Epson printers become some of the easiest to refill.
If your Epson printer is less than about 7 years old, you can find auto-reset refillable cartridges here. The special chips fitted to these cartridges reset the ink level (to full) automatically, every time a cartridge is removed from printer.
If you still use an 'antique' Epson with two ink cartridges - one black and one 3 (or 5) colour, you can find a refill kit for it below. Older Epson (genuine) cartridges were very easy to refill. If the cartridges are chipped, you'll also need a chip resetter to deal with the ink level chips.
Note: Refill kits listed on this page are not made or endorsed by Epson, but you can expect similar results to Epson ink cartridges. All premium dye and pigments included with Epson ink refill kits below are made in USA. Find more ink info here.
Can't find Epson ink refills for your printer on this page?