vinegar no longer sets the dyes used commercially- the chemicals have changed- so unless it is fabric from the 70's or before that method will accomplish nothing. first do a bleed test---wet the fabric- rub it with a white piece of fabric or paper towel & see if it's a 'bleeder' or not. if it is, prewash it with detergent- and check it again- you can add retayne to the water- but synthropol is a totally different 'animal' synthropol suspends the fugitive dyes in the water- so if you had other fabrics in with the red and the red ran the dye would stay in the water- not get on the other fabrics- it does nothing to set dye. but often it is just recommended to keep washing the fabric until it does not bleed any more. some never stop- and then are generally not used in a washable item- some never bleed- some stop with one wash- just test & go from there.