This is a large Volume (4.2ltr) poop bin with a mounting option for two Ø12x3mm magnets which makes the bucket ‘stick’ to the printer's shell (works on X1C as well as P1S, I use this on both).
The bin also should work just fine without any magnets.
I also added a hole pattern at the location of the printer's grid on the back to maintain air circulation.

Further, I added some reinforcements at the top of the model to strengthen the relatively thin walls.
For anyone interested I've also added a version without this bracing, to prevent having to cut them out later.

The Bambu print bed will fit two bins, see images. Make sure to skip the brim, though.
I printed them out of PETG with two perimeter walls which results in a solid wall throughout.

As you can tell from the pictures towards the end of the print I ran out of light grey, happy accident, happens to look cool.