Magical Paint Transfer Cone Widget Thing Free 3D print model
Designed to make transferring paint from awful citadel bottles into awesome dropper bottles a whole lot easier.
I use bottles like this but pretty much all of them have the needed 10mm hole size.
Make sure to print 28mm x 13.29 x 44.03 and it will fit just snug enough to keep it in place. I used a Form 2 at the fastest speed and they come out fine.