I claim the ornamental design for a holdout tube, as shown and described.
FIG. 1 is a front perspective view of a holdout tube showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a perspective view of the holdout tube in an alternate configuration, shown in its environment.
The broken line showing in FIG. 8 represents unclaimed subject matter and forms no part of the claimed design.
The holdout tube is shown broken to represent indeterminate length. The indeterminate portion of the article forms no part of the claim design. Patentability is based only on those portions of the holdout tube that are shown in solid lines.