Swirl it around with your hands (make sure you wear gloves, laundry detergent usually has bleach in it) and make sure at some point every part of the blanket goes under water. My tub is larger than most tubs (lip to lip is just under 6' long instead of 5' long) and it still can't completely fit in at once.
Drain tub
Repeat previous steps with cold water again but no soap this time to rinse it out
