A delightful find on a coolant washer resevoir that was decent on the outside but cruddy on the inside. I used everYthing from bleach to baking soda to try and clean the inside of the coolant side. What I found that worked was to start out dry and pour a cup of childrens toy box sand in close the top and shake violently for as long as I could every time I had nothing to do... like watching TV. It took a while but the sand cleaned it up nice.