Hi Susan, here's a great video that will show you how - https://www.youtube.com/watch?v=rqUsyxL9ClU
There is a product at Home Depot called Spray Nine that works wonders! I've used it to successfully clean all sorts of items (furniture, decking, sinks, etc.) indoors and out. I hope this helps!
I hose mine off and if needed use a soft brush and a mild cleaner like Murphy's oil soap.