By using a siphon tube during water changes.. I have an acid brush on a long fiberglass stick that I use to "dust off" some types of coral just before a water change. Then with the siphon tube I vacuum the dirtiest water and other areas. BUT, my tank is not very old and I seldom need to do this. I do "dust off" some areas fairly often, it helps me feel like a good care taker.
For a "duster", those fiberglass sticks that come with a reflector on the end for sticking up at a drive way or such are perfect. You cut them to length then an acid brush end slides right over them, nice and snugg. The acid brush has a stainless steel sheet metal body rolled to form a tube and flat on the end to mount the bristles. So, it makes a perfect marriage, and the metal won't harm your water chemistry. Acid brushes come in different sizes, I think I'm talking about the ones with 3/8" wide brushes. You can pick a size to fit your stick. In this case bigger isn't better.