The ornamental design for a three-sided diamond whetstone with a basin, as shown and described.
FIG. 1 is front elevational view thereof of a three-sided diamond whetstone with a basin showing my new design where the whetstone is placed in the basin;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a perspective view thereof;
FIG. 8 is another perspective view thereof; and,
FIG. 9 is a perspective view thereo of a three-sided diamond whetstone with a basin showing my new design where the whetstone is separated from the basin.