The ornamental design for a showerheadmanifold, as shown and described.
FIG. 1 is a right side view of a showerhead manifold, in accordance with the present invention, shown in a position of use as connected to a showerhead, a shower arm and a filter cartridge;
FIG. 2 is a top view of the invention;
FIG. 3 is a left side view of the invention;
FIG. 4 is a bottom perspective view of the invention;
FIG. 5 is a rear view of the invention;
FIG. 6 is a bottom view of the invention; and,
FIG. 7 is a bottom perspective view of the invention.
The broken lines shown in the drawings depict environmental subject matter that form no part of the claim.