Every now and then the topic of washing a full fleece comes up in the shop.
All spinners have their own tips and tricks in this regard.
Here's my version...
After picking the fleece for all of the obvious discard I fill a large tub with HOT water and add a small amount of ORVUS paste. This is an agricultural product and should be used with caution.
I'm quite a stickler for wearing gloves (on another topic; I also ALWAYS have a full vapor mask and gloves when dyeing).
My fleece is added to the soap and water. This bath is left for a full day after which I will gently change the water for several repetitions until the bath is clear. The entire wash may take place over a period of two to four days depending upon the fleece. It's a gentle process that I tend to take slowly.
The fleece is transferred to a washing machine and put through a gentle spin cycle in order to speed drying time. I do have a washing machine designated for this task as, over time, lanolin will build up and have issue with any other fabrics that you might like to clean.
I use heavy open (gridded) racks hung over the wash tubs for drying.