Put them in a mesh bag, and set the washer cycle to delicate or light. just like you would for lingerie. The mesh bag will keep the leggings from getting tangled around with the other clothes and keeps them from stretch out. Use warm or cold water, never hot, it does not mix well with the heat. It’s sensitivity to high temps can damage the stretch factor and result in leggings no longer keep everything locked in place. Hang them to dry, or lay them flat on a drying rack. I REPEAT DON’T PUT THEM IN A DRYER, heat is bad news for stretchy fabrics, so let your leggings dry naturally and they’ll last much longer.