The ornamental design for a toilettank, as shown and described.
FIG. 1 is a perspective view of a preferred embodiment of a toilet tank;
FIG. 2 is a front elevational view of the toilet tank of FIG. 1;
FIG. 3 is a left side elevational view of the toilet tank of FIG. 1;
FIG. 4 is a right side elevational view of the toilet tank of FIG. 1;
FIG. 5 is a rear elevational view of the toilet tank of FIG. 1;
FIG. 6 is a top plan view of the toilet tank of FIG. 1; and,
FIG. 7 is a bottom plan view of the toilet tank of FIG. 1.
The broken line showing of the toilet bowl and bottom of the toilet tank are included for the purpose of illustrating a portion of the claim that forms no part of the claimed design.