There two brush cases to choose from. The rectangular case is a friction fit with two halves.
The single brush case fits one brush and screws on with a cap.
Wrap toothbrushes in something like a zip top/lock bag before storing them in these. 3D printers and prints aren't known for their cleanliness.
These have holes in the bottom for air/drainage (there is a version of the single brush case that does not have a hole if desired for some other purpose).
CC0 1.0 Universal