I use one of those cheap lens cleaning kits, the one w/ the little red bottle (mine has lasted 10 years so far!), blower brush and lens papers. Just soak one of the papers (not too much) in the fluid and give it a quick wipe, then another quick wipe w/ a dry paper. Works great. I wonder how mine has managed to last so long? Still perfectly clean water in it too, or whatever the fluid is.