How do you clean the lenses on your binoculars or scopes?  For simple dust and small amounts of dirt, I use a rubber bulb blower or a soft brush, but there comes a time when a more heavy duty cleaning is required.  What do you use to remove water marks from rain or the general crud that builds up over time?
    My Swift Audubons are supposedly 100% waterproof, and I have used lens tissue or cotton balls or Q-tips moistened with tap water, distilled water, rubbing alcohol, and Windex at various times, always with a little fear and trepidation.  I have done the same to our Nikon spotting scope, which makes no claims of waterproofedness.  Is there a better way?  Does anybody know if any of the common solvents dissolve lens coatings?
    Yes, I know that you shouldn't let your optics get dirty in the first place, and you should always use your lens caps, etc., etc., but sometimes a good cleaning is needed.  Any help would be appreciated.
        Larry