The ornamental design for a washboard for washingmachine, as shown and described.
FIG. 1 is a perspective view of a washboard for washing machine, showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a side view thereof;
FIG. 5 is another side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is an enlarged view of the encircled portion 8 thereof in FIG. 1.
The broken lines illustrating portions of the washboard for washing machine form no part of the claimed design. The dash-dot broken lines surrounding the enlarged portion form no part of the claimed design.