Not sure how to get the yellow stains off specifically but when you bathe him (unless you have been directed otherwise by the vet) I would suggest using a fragrance/soap free shampoo. The bully skin is sensitive and you don't want to use harsh soaps, I use Tropiclean Hypo-allergenic Puppy shampoo. Either petco or petsmart definitely carries it but there are other brands available out there I am sure that are fragrance/soap free. Not sure what to do about his poor boils, I guess just keep up on the expressions? Every dog is different, Sam needs his expressed about every 2 months. Samson also has a tight tail that I have to clean to prevent from getting infected. My vet has me clean it with the fort dodge waterless shampoo (spray on a gauze pad or something) then wipe under the tail. Then followed up with wiping under the tail with the mal-a-ket wipes. Hope that helps and I hope Mr. Beefy gets better soon! Poor guy, so glad you saved him! I can't see how a person can allow an animal to get into such a condition.