The citadel water cups are extremely well engineered for the tabletop artist. The only feature I thought they should also have is a brush rack! So here it is. Hope you like it!

I used 3 walls and 15 percent infil.

EDIT: I have updated the rack. It now has a bottom and the brushes can be removed without falling through the rack. It has small water drain holes in the bottoms in case you drop water down the holders.