Dog With Rash Under Tail and Around Anal Area - Please Suggest Remedies

For my now-4 dog rescues, I swear by Nu-Stock - but I make my own for far cheaper. I buy sulfur powder, coconut oil & turpentine, mix it up and its never failed us yet! 2 of them have very sensitive skin so I have had time to use it often.

My recipe: 95% sulfur powder, enough coconut oil to get it to a smooth texture, and about 2% turpentine. I don't know the size of the container you would mix it in, so that's why I only gave percentages. Recently, I actually was out of both c.o. and turpentine, so I used some vicks vaporub (it has some pine essential oil in it) and mixed it with some of the sulfur powder; my lazyman recipe. But it worked in a pinch for a few days.