Tell us about yourself!
Both gm280 and CheesesOfNazereth are correct about using an acid brush. These are called acid brushes because they are acid resistant so they can be used to brush acid. I've seen them in many shapes from tooth-brush shaped to the picture provided by CheesesOfNazereth.One trick that I've found with the type shown above is the bristles are too long for scrubbing. I've used cable cutters (the type with the two curved blades) to cut the bristles down to 0.5 to 1cm long. Then they work really well for scrubbing flux deposit off splices and PCBs (along with generous helpings of alcohol).
The Triptych - A Portable Arduino Workshop
Digital multimeter shield for Arduino
Cheap and effective Sous Vide cooker (Arduino powered)
DIY Compound Gin