Hi, sorry is your piggy a he or a she? if it's a he it's probably it's grease from his grease land building up, to clean that then you can use a little swarfega gel or dishwashing liquid to break the grease down then rinse it with warm water. If it's poo then just rinse it wish warm water and that should soften it enough to rub out.
Id always reccomend cutting long haired piggies hair very short around their bottom, i give my sheltie an undercut so he doesnt get all mucky![]()
how is she doing? as the diarrhea stopped?