this DOES work clean all dirt grease off etc with washing up liquid, then in a warm mildish bleach (yes bleach) leave them for a couple of hours...they should come quite clean...you may find a very small amount of the surface comes off too ...rinse in clean warm then cold water and dry off....i have 2 pairs off these that have been left hanging in the unheated shed for 2 years and they haven't gone discoloured or anything....now for the health and safety,.try on a scrap one first though watch your clothes and wear gloves.
steve chambers
chesterfield
england