The ornamental design for a filling portstructure for a flexible, multiple chamber storage container for medical use, as shown and described.
FIG. 1 is a front view of the filling port structure for a flexible, multiple chamber storage container for medical use;
FIG. 2 is a rear view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a left side view thereof; and,
FIG. 6 is a right side view thereof.
The environment, consisting of a flexible storage container for medical use, shown in broken lines in FIGS. 1 through 6, forms no part of the claimed design.