FIG. 1 is a front perspective view of a flask, according to my new design;
FIG. 2 is a front facing view thereof; the dashed lines of FIGS. 1 and 2 representing a label, the latter of which is not part of the claimed design;
FIG. 3 is a right side elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a rear facing view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.