I was doing a project with urathane, and after applying it to several large pieces, I had a very messy brush. I spent twenty minutes plus trying to clean it using paint thinner, and running water. I thought I was successful, but when the brush dried, it was hard enough to be unusable. Is there a trick to cleaning urathane off brushes that I'm missing, or do I just have to use more paint thinner and time?
John