I'll agree with the others about Technu. I buy the two bottle packs. The first bottle is the one everyone described above. I keep one of those in every truck and trailer and around the shop. The second bottle is simular to calamine lotion to stop the itch, but works much better.
The first bootle that removes the oils, I have used it as late as a couple days after exposure once blistering had started.
Why do people not respect us as they do other tradesmen? Because every Tom, Dick, and Harry doesn't think he can be a plumber or electrician!