You can either buy a new waste toner box - or take the full one out, empty it yourself and put it back. I've already done the latter twice - but it's dirty work - the contents are dusty and can hardly be cleaned away.... It's best to wear a mask and disposable gloves and not in the living area...
I also had to replace an image drum recently: Every print had black streaks...
This can have various causes:
https://www.tonerpartner.ch/laserdrucker-druckt-blass/
https://blog.hd-toner.de/laserdrucker-druckt-schwach-was-kann-man-tun-bei-blassen-drucken/
https://www.aw-print.de/laserdrucker-druckfehler
Try to get to the bottom of the problem. After that, you can always replace the drum unit.
Hello. Yes, it is also listed as an accessory with the printer and if you search for the drum unit for the SL-C480W at other toner suppliers you will also find this...
I only replaced the unit when the quality decreased. You can take out the container and simply empty it. Then wash it out well and let it dry. But it takes quite a long time until it is full. It depends on how often you print. Half a year doesn't seem normal to me.