I would not bother to even put it in the tub. I would just fill the washing machine with warm or maybe hot water and let it soak. (My machine has a handwash cycle so I would use its rinse cycle but if you don't have that, just let it soak in the tub with no agitation.) Then drain and do a second soak if desired. This saves having to move the wet batting. Then use a slower spin cycle if possible to get out most of the water. Then dry in the dryer as suggested above.