I was a bit frustrated that I was not able to get the tips ungunked. Then after doing some reading up on Ravelry I got the idea to do an ammonia wash. I did another wash this time adding some ammonia to the water. Then I did a few rinses, adding vinegar to the last. I also left it to soak in its final rinse overnight.
After drying and combing out the tips the wool is a bright beautiful white. I was very happy with the result.