These are the most simple cartridges to refill. You will need a syringe and a bit of fish tank air hose. You can pick the air hose up from your local pet shop.
Get your air hose and fit it over the end of your syringe then cut it off and leave around 2 or 3mm of hose at the end. Fill your syringe with 40ml HP Black Pigmented ink. Next place the syringe over the print head using the air hose to make the seal then slowly push the ink into the cartridge.
These cartridges have a bladder inside them this is what make them leak once you have filled them so you must deflate the bladder again once you have filled the cartridge. To do this you put your empty syringe back over the cartridge print head and suck the bladder back into place. You might have to do this two time for it to work.
I am having difficulty with HP 364 carts after refilling with the correct Inktec Ink either using the supplied clip or tried one with the German method. I get the ink in ok but the Printer continually warns me 1. Ink is low when obviously it is not or 2. I have installed used carts (I did buy some used unfilled XL on E-bay) they looked fine. They also warn output might not be very good They are right output is very mixed Print quality report shows missing Cyan streaky Black. Perhaps you should only refill new ones when they run out. I believe Pharmicist mentioned something like this. However I have spent hours and quite a bit of money fighting this HP Phtosmart C5380 and feel the only way around it would be to fit refillable carts but the only ones I have seen are again on E-bay and probably of Chinese orign. Any ideas from this knowledgeable Forum would be appreciated.