The dryer won't set the color, but wouldn't it be nice if it did? The color catchers are used to catch the color so that it doesn't get onto other fabrics, but if you're just washing the batiks I would think it's a waste of money to use them, except that they let you know whether there's still excess dye there. I would let the fabric sit for a long time in very hot water, rinse, repeat, until the water runs clear.