According to a tweet from Brandon LeBlanc - the Senior Program Manager for the Insider team, the ISO files for Windows 10 Insider build 16278 are now available. The build was pushed out to Slow Ring Insiders a couple of weeks ago, but its availability as an ISO file now gives all Windows Insiders the opportunity to clean install it on their PC.
— Brandon LeBlanc (@brandonleblanc) September 19, 2017
You can find the build right over here, on the advanced Windows 10 Insider Program page. In order to grab the ISO file for Windows 10 build 16278, just click on the drop-down menu on the bottom, and select the build up on the top of the list As always, you should carefully consider installing these on your primary computer, as they're not always perfectly stable.