This is a bucket to use watercolor with a Uuna Tek IDRAW H A3.

In PLA and coated with a layer of UV resin to make it waterproof and hooked with magnets. I place under a larger piece of transparent plastic sheet to avoid projection of paint if brush touch the bucket. I fill bucket with watercolor from tubes.
Idraw have a limited up/down position of pen which is not very high so buckets needs to be low and under this limit. Max height in Inkscape settings.

2 buckets can be nested together to prevent slipping (color and water)

Example in video
https://www.instagram.com/p/C-Znl04MmRh/?img_index=1