i'm not quite sure if this recipe will work mange, but it works wonders on my dog's seasonal dandruff:
1. shampoo your dog with coal tar shampoo, you can get this at any pet supply store. be sure to work into a good lather and SCRUB!
2. rinse completely, let your dog drip-dry for a few minutes
3. dilute 3 parts listerine/sea breeze/ anything antiseptic to 1 part water. work into your dogs fur, making sure it coats the skin. let stand for about a minute
4. rinse well
5. tar shampoo one more time if necessary
6. let your dog drip-dry. dont use a dryer, it will dry his skin out.