The ornamental design for a portion of toilet, as shown and described.
FIG. 1 is a perspective view from above of a portion of toilet showing my new design;
FIG. 2 is a front elevational view;
FIG. 3 is a back elevational view;
FIG. 4 is a right elevational view, a left elevational view being a mirror image thereof; and,
FIG. 5 is a top view.
The broken lines represent environmental subject matter and form no part of the claimed design. Lines shown on product surfaces are shade lines and not surface decoration.