The Canon MX475 uses the combined sponge/printhead cartridges PG-540 and CL-541. These are much more difficult to refill than the single ink tank cartridges. My guess it that they can be refilled around 5 times if you are lucky.
Your chances of a successful refill will be better if you refill at the first signs of ink starvation or even before, by keeping the cartridges topped up. I don't know how many times the cartridges can be refilled, but even a few times saves money.
An alternative to refilling is buying commercially remanufactured cartridges, but the price should be less than 50% of the price of new OEM cartridges IMO, else I think the OEM cartridges are preferable.
Notice that the druckerchannel staff had problems with loss of cartridge capacity after a number of refills of the black cartridge.
I have sometimes saved a dry cartridge, both Canon and the very similar cartridges from HP by removing the lid and removing and washing the sponges. The cartridges without sponges can now be cleaned like you would clean a Canon separate print head. After cleaning the print head the cartridge can be reassembled with the cleaned sponges and refilled and primed. But this is difficult and I think my success rate is below 50%.
Using Google to search for the cartridge type used in the Canon MX475 I stumbled upon a "rebuilding kit" for the cartridges. The kit contains replacement sponges in plastic cassettes for the cartridges. I think the cassettes can be refilled by drip filling from the bottom. Has anybody tried this "rebuild kit"?