By the nature of waterproof and breathable, wash them inside out, if you have a hand or wool wash option on your washing machine that is below 40°C this is best.
There are no special requirements for the type of washing powder or detergent used.
Let them drip dry naturally inside and then out, avoid drying on a radiator or other direct heat source to prevent damaging the waterproof membrane. You can tumble dry on a temperature low setting if you require.
Always wear appropriate footwear. Inspect the inside of your footwear for stones, thorns and other sharp objects that could damage the waterproof membrane.