Did you refill with this method?.......
http://www.inksupply.com/51645a.cfm
If so make sure the ball bearing is sealed tight, you may put a piece of black electrical tape over the ball bearing to help with the seal. If the cartridge is sealed properly, and still leaks, then I would suspect it...
They fill the same as most HP cartridges, HP27,28,56,57, 75 and 90 series, here are the instructions for the 75's, just do the same for yours, ink capacity may be different, so watch that.
http://www.alotofthings.com/viartshop/article.php?category_id=11&article_id=491
Yes you can flush out the cartridges, there are several posts about this in this forum you can start here........
http://www.nifty-stuff.com/forum/viewtopic.php?id=1310
As for flushing the print head, this is a very delicate operation, also on this forum, you can start here...
Always use ink made for the cartridge it's meant for, Not all ink is the same.
Also, if you bring in an empty old dried out cartridge to a commercial refiller, they will assess whether it can be refilled, if it can't it should be sent away to be recycled another way.
I can recommend Atlantic Inkjet for online orders. There is a place on Ebay called PrecisionColors, that sells bulk OCP ink, which is one of the tops in quality, I am not sure if they sell HP inks. I have heard Hobby Colors is good. There are others on this forum besides me that can recommend...
Have you tried Ebay? or Atlantic Inkjet?
http://www.atlanticinkjet.com/recycled-cartridge-canon.asp#cartridge
And I am sure there will be other suggestion coming from other forum members
Being that you refilled right away, I would suspect the ink quality is not good. There is alot of low quality ink refill kits out there, and not alot of people know enough not to buy them. If you list area you reside, then I am sure someone on here will point you in the direction of a High...
"The non-oem cartridges don't even have a pressure valve on them just a vent hole at the top."
How interesting, I've never seen those kind, the ones I sell to my clients have the relief valve. I wouldn't know if the ones you are talking about are any good or not, seems strange not to have the...
http://www.atlanticinkjet.com/default.asp?Nation=US for your ink and supplies
As for tutorials, go to http://www.nifty-stuff.com/forum/viewtopic.php?id=2465