I claim the ornamental design for the can drainer, as shown and described.
FIG. 1 is a top perspective view of the can drainer, showing my new design;
FIG. 2 is a top view of the can drainer;
FIG. 3 is a front view of the can drainer;
FIG. 4 is a back view of the can drainer;
FIG. 5 is a left side view of the can drainer, the right side view being a mirror image; and,
FIG. 6 is a bottom view of the can drainer.
The broken lines included in FIGS. 1, 2, and 6 represent a magnet secured to the can drainer and are for illustrative purposes only and form no part of the claimed design.