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It will usually say on the butt end.

I understand vinegars cleansing properties, but will it hurt the hair in any way? Such as bleaching it out, ruining glue that binds the knot, etc.

BTW, what does the borax do?

Anti bacterial hand soap should do the trick. Work a good lather up with the brush making sure the soap gets everywhere within the brush, let it sit and allow the soap to do its job, rinse...