Flatten
Reference
Mode:
Sculpt Mode
Tool:
Toolbar ‣ Flatten
Flatten or contrast surfaces by pulling and pushing them towards (or away from) a defined medium height. This medium height is determined via an area plane within the brush radius.
This area plane height can be further defined in the brush settings.
Brush Settings
General
Direction Ctrl
Invert the direction to push surfaces away from the sculpt plane, creating more surface contrast as a result.
Note
More info at General brush settings and on Advanced brush settings.