Brother HL-1000 - Manual (Page 43)

CHAPTER 5 MAINTENANCE
5-5
5. Install the new toner cartridge into the right hand side of the drum
unit. Make sure that the toner cartridge guide bar is exactly aligned
with the guide slot in the drum unit and pushed fully home into the
drum unit to ensure that the toner cartridge and the drum unit fit
together correctly.
Fig. 5-7 Installing the Toner Cartridge
into the Drum Unit
6. Gently turn the lever on the toner cartridge backward until it stops.
Fig. 5-8 Turning the Lever to Open the Shutter
7. Turn the drum unit upside down gently.