The ornamental design for a post for bath accessory, as shown and described herein.
FIG. 1 is a perspective view, taken from the front, top, and right side of a post for bath accessory showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear front elevational view thereof, the phantom lines showing the post for illustrative purposes only and forming no part of the claimed design;
FIG. 4 is a left side elevational view thereof, the phantom lines showing the post for illustrative purposes only and forming no part of the claimed design;