We claim the design for a drop in sink, as shown and described.
FIG. 1 is a top front right perspective view of a drop in sink of our design;
FIG. 2 is a top plan view thereof, the bottom plan view being plain, unornamented and unclaimed;
FIG. 3 is a front elevational view thereof, the left, right, and rear elevational views being identical thereto, the dashed lines representing unclaimed features; and,
FIG. 4 is a cross sectional view taken along line 4-4 in FIG. 2, the dashed lines representing unclaimed features.