Does a laser toner cartridge have to be empty before refilling?

"If you are refilling with cheap toner into a genuine one, you are probably best off emptying as it will be different and you may have a lot of imperfections when they mix.

If you are topping up one that has already been refilled, I would say the answer is no because it is the same stuff.

Just be careful if you do this to much as they may change the consistency or formulae between batches/bottles.

Lastly, make sure it really is the toner you are emptying and not the waste toner or similar as this would have to be emptied each time.

(Out of curiosity, what printer/cartridge is this?)"