I’ve never used anything on my diamond stones during the sharpening process. Maybe once a month (10-15 knives) I’ll clean ’em with a spray bottle of isopropyl alcohol. However, I clean my diamond films with the same alcohol maybe every other knife.
I’ve always felt (probably wrongly) that using a liquid during sharpening would actually turn the swarf to mud and help it to clog up the diamonds. But I could just as easily make an argument that using a liquid during sharpening could help to wash away contaminants. With a totally dry process, the swarf seems to fall away on its own. I use a Swiffer duster to clean the edge for microscopic inspection. It works so good I think it might work for cleaning the stones of metal dust.