The ornamental design for a diptubeendfitting, as shown and described.
FIG. 1 is a top side perspective view of a dip tube end fitting according to the present invention.
FIG. 2 is a side view of the dip tube end fitting according to the present invention.
FIG. 3 is a top view of the dip tube end fitting according to the present invention; and,
FIG. 4 is a bottom view of the dip tube end fitting according to the present invention.
The broken lines showing a base for the dip tube end fitting are included for illustrative purposes only and are not meant to be part of the claimed design.