It's worth giving the toner a shake before you actually change the cartridge. Just a gentle backwards, forwards and rotate to loosen the remaining toner up. I used to look after several dozen assorted printers around our office block and it always worked for me.
N.B. - You have to be gentle as the toner itself is pretty noxious stuff so you don't want to risk it leaking.
At one office I was in, the IT department were "complaining" about the amount of cartridges being used and the cost - which was ultimately billed to the teams based there. They then decided to implement a policy that only the IT team would change cartridges in printers and fax machines rather than leaving spares with each. The policy was that when printer was reported a technician would remove the cartridge, and shake it horizontally, then put a small white Tippex mark on it and this would continue until there were something like 5 marks and at that point the cartridge would be replaced. The toner bill dropped by well over 50%.
The shake just needs to be a couple of taps to start then a gentle left right to redistribute the toner - just think about a page the left most 2 cm are never used (or very rarely) and as you go to the right general usage also drops so there will be empty and full parts.
M H C
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