We recommend hand washing your knee sleeves with water or a mild detergent (or a specialist neoprene/wetsuit detergent), then allow the sleeves to air dry standing up.
The spin cycle of a washing machine can damage the sleeve, as the knee sleeves become quite bulky when wet and can potentially get caught up or damaged by wringing. High heat from a washing machine or a dryer will degrade the rubber in the sleeves (potentially causing shrinkage or brittleness).