If I have something dirty I wash it before I flesh in water with a little detergent in it.
Greasy furs like otter, mink, civets I have a drum and drum them in 1/8"corn cob grit after fleshing.
Bobcats I dry wash in borax and blow out with a compressor. This is after they are dry.
A good brush and hanging in front of the fan helps too.
That is to sell them but if I am sending to the tannery I don't do much except wash blood out prior to drying.