The ornamental design for an outlet for a diffuser, as shown and described herein.
FIG. 1 is a top perspective view of an outlet for a diffuser;
FIG. 2 is a front elevational view of the outlet of FIG. 1, wherein a rear elevational view of the outlet is identical thereto;
FIG. 3 is an elevational view of a first side of the outlet of FIG. 1, wherein an elevational view of a second side of the outlet opposite the first side is identical thereto; and,
FIG. 4 is a top plan view of the outlet of FIG. 1.
The subject matter shown in the figures above in dashed lines forms no part of the claimed invention.