The iodine I buy (it's a standard human and animal antiseptic over here for everything from washing wounds to treating ringworm to washing hair and body in hospital prior to operations) comes in two strengths: iodine (Betadine) 4% which is a handwash or scrub and lathers up and Betadine 10% which is daubed undiluted (or not further diluted) on wounds, things like ringworm, etc.
The vet has told us to use it on wounds on our animals (cats and dogs) too. I think there's a vet version - Vetadine.
Anyway, for abcesses, I'd use the 10% version but if you buy it from the vet they'll advise you on usage.