The ornamental design for a bassinettub, as shown and described.
FIG. 1 is a perspective view of the bassinet tub embodying my new design;
FIG. 2 is a left side view thereof, the right side view being a mirror image thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a front view thereof; and,
FIG. 6 is a rear view thereof.
FIGS. 1-6 show portions of the bassinet tub in broken lines. The broken lines are shown for environmental purposes and form no part of the claimed design.