The ornamental design for a tubfiller, as shown and described.
FIG. 1 is a front perspective view of a tub filler showing my new design;
FIG. 2 is a right side view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a front view thereof; and,
FIG. 7 is a rear view thereof.
The broken lines immediately adjacent to the photographic area define the bounds of the claimed design and form no part thereof. The broken lines depicting the remainder of the tub filler show features that form no part of the claimed design.