Caran d'Ache Museum Aquarelle Waterbrush Pens - Set of 3
To fill this brush pen:
1) Unscrew the brush tip/grip of the pen, dip the barrel in water, and pull back on the piston.
2) Reattached the brush tip/grip.
3) Turn the barrel right side up so that the brush tip is facing up, and the piston pointing down.
4) Push the piston slowly back into the pen.
For max capacity, you can push the excess air out of the barrel after filling the first time, then fill again.