I made a simple refillable charcoal box for the Bambu Lab X1 (may fit others) so you can buy charcoal pellets and refill the filter instead of buying new ones. I made model solid, so you need to set top and bottom layers to 0, then pick you internal infill pattern of choice.

I did 35% Triangle infill with 5 walls to cover all the overhangs in the model.

You can use a piece of tape to give a pull tab to easily remove the filter from the printer.

Please let me know if you have any issues or need any help with yours.