Use the washing machine. If the lines are so bad that the washer is going to cause abrasion problems they probably need to be replaced in any event. However, I usually don't see washers with anything but rounded corners, so abrasion should not be a problem.
Put them in something to prevent the spaghetti effect. Either a mesh bag or a pillow case works just fine. Mild detergent, and downy smells nice and makes them softer
. Hang them to dry them!