The ornamental design for a powerwasher, as shown and described.
FIG. 1 is a perspective view of a power washer of the present invention;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is an bottom plan view thereof.
The broken line showing of details in FIGS. 2, 3, 6 and 7 is included for the purpose of showing environmental portions of the power washer and forms no part of the claimed design.