The ornamental design for a base of an endoscopetip attachment, as shown and described.
FIG. 1 is a top, front, right perspective view of a base of an endoscope tip attachment, showing our new design, where the base of an endoscope tip attachment is shown with the unclaimed endoscope inserted;
FIG. 2 is a bottom, rear, left perspective view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a right side elevation view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken lines of even length shown in the drawings depict portions of the base of an endoscope tip attachment that form no part of the claimed design. The uneven length broken lines depict the boundary of the claimed design and form no part thereof.