I claim the ornamental design for a toilet tank, as shown and described.
FIG. 1 is a perspective view of an embodiment of the claimed design;
FIG. 2 is a front view of the embodiment of the claimed design shown in FIG. 1;
FIG. 3 is a rear view of the embodiment of the claimed design shown in FIG. 1;
FIG. 4 is a side view of the embodiment of the claimed design shown in FIG. 1;
FIG. 5 is another side view of the embodiment of the claimed design shown in FIG. 1;
FIG. 6 is a top view of the embodiment of the claimed design shown in FIG. 1; and,
FIG. 7 is a bottom view of the embodiment of the claimed design shown in FIG. 1.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design.