There is a situation that concerns most HP refillers. In our refilling instructions we use a suggested amount of ink that TYPICALLY will sufficiently charge cartridge without overfilling it. This is just a guide and sometimes an overfill can occur. What do you do then? When you overfill a cartridge there is a great risk of one color overflowing into chamber of color next to it resulting in cross chamber contamination. It can definitely cause a quick death to that cartridge if it is excessive.
The best thing you can do is try to siphon all ink out of cartridge with your injector and inject a cleaning solvent. Siphon out solvent, rinse and repeat as necessary.
This can be very time consuming so a little bit of preemptive measure may save you a lot of time and frustration. Lets examine some of things that can be done to prevent this in first place.
By inserting a toothpick into refill holes, or vent holes, you can get a better gauge of how much ink is in each chamber. Use a new toothpick in each chamber so you don't contaminate ink. Keep in mind that HP "D" cartridges only hold 19ml of ink, half that of an "A" cartridge.
Another gauge would be more difficult but a lot of people report success using it. This is "page gauge". You can keep track of how many photos you print (or any print that uses a lot of color) and when you reach a pre-determined number of pages you know it's time to top off your cartridges. Each user will have a different page gauge depending on their usage and it make take a little while to figure out what it is for your particular situation.