You can buy a little gadget on Ebay called a chip resetter. With this you can reset the cartridge chip so it shows full again, and you can actually use all the ink in the cartridge.
You'll be surprised how much ink you normally throw away.
Note that you need to have a new cartridge on hand. When any of the ink colours starts to fade you need to replace that one straight away to avoid ink in the jet of the printer head drying out. This would block it and with Durabrite ink it is not easy to fix.