Nasty eye stains? How do you deal with them??

Hey! I recently visited my sister and she was really concerned about her 2 yo Bichon which recently started having stain marks below his eyes. She did went to the vet and he recommended just cleaning the area around the eye with wet towel every morning. 2 weeks later it's still the same. This really got me interested what people are doing to stop it, of course she already scheduled a vet visit but I just had to do my own research as well :flypig: Thank you in advance!