Clean a large sumac cluster and remove any kind of extra sticks or leaves clinging to them. Break the drupes and remove the sumac berries from the sticks. Place these berries in a bowl with 2 cups of cool water and crush the berries using the back of the spoon or a potato masher. Let them sit for 6 hours or overnight in water. Strain the water using a fine mesh strainer and use it to make the lemonade.