UPDATE 2020: Simplest method of all…while painting, hold down the TILDE key: ` (usually at the top left of your keyboard while you are painting and your brush will turn into an eraser, with all the same properties, as long as you hold it down)
If, like me, you loved being able to select any tool (usually the eraser) and then pick from your most recent brushes to convert a paint brush to an eraser, or a mixer brush, or a smudge tool with all dynamic setting intact you can’t do this anymore with the latest Photoshop update (v 19) You can still use the clear mode trick to convert your brush to an eraser which I go over in the aboce video inclusing the keyboard shortcuts.
The keyboard shortcut I use in the video are
Clear Mode (eraser mode)
You can find the full list of brush mode keyboard shortcuts on the Adobe website here It’s a long list so search the page for “Use for blending modes”