The ornamental design for a combined dishbrush and sponge, as shown and described.
FIG. 1 is a front isometric view of a combined dish brush and sponge in accordance with the new design;
FIG. 2 is a left side isometric view thereof, a right side isometric view being a mirror image thereof except for the bow detail; and,
FIG. 3 is a rear isometric view thereof.
The broken lines shown in FIGS. 1-3 are for the purpose of illustrating portions of the combined dish brush and sponge that form no part of the claimed design.