Square Drain Extension

FIG. 1 is a bottom plan view of a square drain extension, showing our new design;

FIG. 2 is a back side elevation view thereof; the front, right and left sides being an identical image;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom perspective view thereof; and,

FIG. 5 is a top perspective view thereof.

The broken lines shown in the drawings depict portions of the square drain extension that form no part of the claimed design.