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Find a tub or basin large enough for your blanket to fit in and fill it up with cool water. Mix in mild detergent and let it spread through the water. You'll essentially be doing the same thing as a washing machine on a gentle setting, only manually, which gives you greater control over how the blanket is treated and helps ensure that every part gets clean. Don't fill the tub up too much or it may overflow when you put the blanket in. Using soft, kneading strokes, drag the blanket back and forth in the soapy water. It's best to take hold of one section of the blanket for a few passes, then smooth it out and wash a new section. Do this until the blanket has been cleaned thoroughly. Take the blanket out of the tub and let the saturated water run out. Fold the blanket in half two or three times and then use both hands to apply pressure to the blanket, squeezing out excess water. Pressing the blanket is a safer alternative to wringing it out, which can stretch the fabric out of shape. Give the blanket another quick wash in some plain cool water. This will rinse away any detergent that might have soaked into the blanket. Swish the blanket through the water, touching each section individually. Make sure there are no traces of soap remaining on the blanket.  Drain and refill the tub with fresh water until it remains clear after rinsing. You may need to do this several times. Make sure you hand wash delicate fabrics like wool, silk and linens. These fabrics are woven from natural fibers and may be irreparably damaged if treated with harsh washing methods.
Fill a tub with cool water and add detergent. Swish the blanket through the water. Press out excess water. Wash again using plain water.