What seems to be most frustrating thing to refillers is probably most easiest thing to remedy. The problem is many people don't have patients to do it this way. I'm talking about gravity refilling. One of biggest problems facing refillers is injecting ink too fast into cartridge. This causes tiny air bubbles to get into sponges, I call them micro bubbles. When one of these "micro bubbles" hits print head it will cause missing print and/or streaking. Also you may notice that it will print fine one day and next day it won't print until you do a series of head cleanings. Sound familiar?
Gravity refilling is a simple procedure and I will explain how to do is in a minute. Cartridges best suited to gravity method are those with a primarily sponge filled interior. Examples are HP C6578, HP C1823, HP C6657, HP C8728, HP 51649A, Lexmark 18L0042, 12A1970, 12A1980 and most Epson Cartridges. Epson cartridges have another advantage that I will cover and that is ability to use BFILL adapter.
Prior to refilling any Epson cartridge you should use a BFILL to suck out all foamy ink. A BFILL adapter is a small plastic attachment that fits on end of your injector. It fits snugly into ink ports on bottom of Epson cartridges. After sealing any filling holes use this to suction out foam.
Using gravity method is no different than normal refilling with a few exceptions. The ink is still going into same place but how it gets there is a different matter. To do this you need two ink injectors. Remove plunger from one of injectors. The plunger is part that you push on with your thumb when injecting ink. Use a three inch needle or longer with large HP cartridges.