I let it soak in the warm, soapy water for around half an hour. I then drain out the soapy water and put in fresh, warm rinse water. Drain that water out and repeat the rinse step once more. After the second rinse, let the machine spin the whole thing. I like to do this on a warm day so that I can take the fleece outside and unroll it to dry in the sun.
Most spinners card their wool.
That works quite well for the wool from most breeds of sheep and also works well for Shetland wool. However, Shetland wool varies a great deal from one fleece to the next. Sometimes the tips will be a different color that near the skin. This could be from sun bleaching or from a natural change in pigmentation, especially with a lambs fleece. I prefer to gently comb each lock with a dog comb.