For reasons known best to Apple, the Disk Utility app in OS X El Capitan has been overhauled and several useful features removed. People have been struggling to create USB sticks compatible with Windows, and can no longer scan operating system files for permission errors. The ability to secure wipe a disk has also gone.
There are a handful of hacks to restore the older Yosemite version of Disk Utility within El Capitan but, it transpires, most of us have access to an earlier version of Disk Utility with no need to hack anything. In fact, it’s just a few key presses away.
See today’s earlier post about Internet Recovery and, in particular, the section describing how you’ll boot into the version of OS X that was current when your Mac was manufactured. Unless you bought your Mac after 30th September 2015, booting into Internet Recovery will provide access to an older version of Disk Utility with all the goodies mentioned above still present.