Dell 720 Owner's Manual page 25

Store the cartridges in an air-tight container or dispose of them properly.
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If you are installing new ink cartridges, remove the sticker and transparent tape from the
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back and bottom of each ink cartridge.
NOTE: You can use your printer with one cartridge (color or black) at a time. To extend the life of
your color cartridge and improve printing speed, install both a color cartridge and a black cartridge
at the same time.
Ink Cartridge Maintenance
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