My current work printer, an HP something or other, does not have the
inkjets in the cartridges. I only use black ink and so only refill the
one cart. Instead of drilling a hole I add the ink through the
absorbent pad on the bottom of the cart that delivers ink to the
printer head. I add ink one drop at a time and it is fascinating to
watch it soak in. The ink spreads across the complete pad surface
almostly instantly and then soaks in almost as fast. As the cart gets
fuller the ink is absorbed more slowly so it is easy to tell when the
cart is almost full. Much easier than my home printer where I have to
add ink through a drilled hole using a syringe.
Eric


For the usual padless carts I use a length of spaghetti tube as a
dipstick , when filling from syringe, rather than cc markings on the
syringe.

There seems to be a hydrophobic surface to the nozzle plate of these
carts, I suppose some sort of nano material coating