I put this lovely bowl in my guest bathroom, but now I'm having trouble keeping it clean. I dry it after every use but haven't been able to get everyone else to do the same. Now it needs cleaned, but I'm unsure how. I shined the rim with a metal polish, but there are still marks on it if you look close and I'm starting to see a white film in the bowl. I have requested a user manual from Elkay with no response so far, so I made a 2nd request today. Any ideas?