FIG. 1 is a perspective view of the internal filter showing my new design; FIG. 2 is a front plan view thereof; FIG. 3 is a back plan view thereof; FIG. 4 is a right plan view thereof; FIG. 5 is a left plan view thereof; FIG. 6 is a downward plan view thereof; and, FIG. 7 is an upward plan view thereof.