FIG. 1 is a perspective view of a leaching chamber comprising of the ornamental design of the present invention; FIG. 2 is a side view of the leaching chamber of FIG. 1, the opposite side view being a mirror image; FIG. 3 is a front view of the leaching chamber of FIG. 1; FIG. 4 is a rear view of the leaching chamber of FIG. 1; FIG. 5 is a top view of the leaching chamber of FIG. 1; and, FIG. 6 is a bottom view of the leaching chamber of FIG. 1. The broken line showings of FIGS. 1-6 are for illustrative purposes only and form no part of the claimed design.