I work with about 4 or 5 ounces at a time. Running the hottest tap water that I can, I add a couple squirts of Dawn dishwashing soap, then gently sink the fiber in. I let this soak for about 20 minutes, every once in a while giving it a few pokes. I lift the fiber into a colander and drain out the dirty water. You will be amazed how filthy this is compared to the fairly clean look to the fleece. I repeat this wash, usually 2 washes are enough. Two rinses should finish it up.
I have never had my fleece felt but I think that it's important to know that you can go from cool to hot, but NEVER hot to cold......and as little handling and agitation as possible.
After washing and rinsing the fleece, I put it into mesh bags, and using the last spin cycle on my top loading washing machine, I spin it out. This cycle adds no water so my fiber is safe.
It will come out of the bags rather clumpy, so I pull it apart and sort of line up the fibers, and spread it on my counter to dry. By now most of the vegetation has disappeared and I pick out any remaining, along with second cuts that might have been missed.
Mira and Lyra's fleece is drying. Tomorrow I will show you how I'm going to card these two colors together.
Aimee, I would think that you could do the entire fleece in the bathtub, or even your washing machine, if you didn't agitate. I just don't like lugging around that much wet fleece.