You can usually get away with refilling toner in a drum unit of that size 3 or 4 times before the drum, cleaning blade or mag rollers go bad. The toner side will have the larger cavity usually with a glued on lid or cap on the top or side someware. The HP will have a waste toner cavity on the opposite end of the drum unit. If there is no lid on that side, drill a small hole in a safe spot and dump or blow (MESSY) it out. Cover the hole(s) with tape afterwords. I think the canon also has a built in waste toner. If not the bottle is under the back panel. Just be careful you don't scratch the drum or expose it to direct lighting for too long or else you will have to buy a new unit either way. Look into remanufactured units too. Lots of good prices on those popular machines. Sometimes the headaches are not worth the savings.
Good Luck!
Adam

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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320