I'm pleased to hear that someone else refills their cartridges.
Most people don't seem to think it is worth the effort but I've refilled mine for over 12 years now. It takes about 20 to 30 minutes to do both the black and colour and saves a fair amount of cash.
I recently refilled the same HP cartridges for just over two years and the total cost of the ink was roughly £5.
On an unknown cartridge I always use a wooden cocktail stick to check the colours before filling but your regular cartridge will always be the same layout.
If the ink floods out of the print head it just means that the ink level is now above the top of the Felt so withdraw about 1 cc and then wipe the print head with a paper tissue.
This can be a useful web site to know about.
http://secure.stratitec.com/lookup_step1.php
Good luck, Divegirl.