Lavatory basin

The design is the visual features of the LAVATORY BASIN shown in the drawings, whether those features are features of one of shape, configuration, ornament or pattern or are a combination of any of these features. The stippled lines are provided for illustrative purposes only and form no part of the present design. Drawings of the design in eight (8) views are included, in which: FIG. 1 is a front, raised perspective view of the LAVATORY BASIN, in accordance with the present design; FIG. 2 is a front view thereof; FIG. 3 is a rear view thereof; FIG. 4 is a top view thereof; FIG. 5 is a bottom view thereof; FIG. 6 is a right side view thereof; FIG. 7 is a left side view thereof; and FIG. 8 is a rear perspective view thereof.