How you wash it depends on if it is wool or acrylic. It will be very heavy wet and hard to lift or squeeze in the bathtub. My back would not be up to that chore. Perhaps an acrylic afghan could be washed at a laundromat on gentle cycle? I do not use laundromats so I cannot speak of how their machines might treat this item. For wool washing I would go to the Laundry Room forum for info. There are some real experts over there.

Laundromats tend to have one super big washing machine. I would use one of those to wash an acrylic queen afghan. Use gentle, and be sure to use fabric softener if it is acrylic to eliminate the static shock factor. You might want to check the inside of the machine to be sure it is clean. Around here, folks have horses, and those machines get used for horse blankets and also for large, washable rugs.