you do the following.
Get a small plastic bottle that is impervious to Acetone.
Drill a small hole in the cap, smaller than the middle diameter
of the brush.
Pull the brush handle up through the cap until it is very tight.
Fill the bottle with Acetone until it is above the bristles of brush.
You can now screw the cap on and the brush will stay straight,
clean and soft.
Clean out the bottom of the bottle about every 10 baits.
And refill with fresh Acetone.
The pictures tell it all.