The ornamental design for a drainholder, as shown and described.
FIG. 1 is a perspective view of the drain holder of my new design, showing it situated on the body of an individual with a body drainage container placed in a pocket thereof.
FIG. 2. is a front elevational view thereof.
FIG. 3 is a back elevational view thereof.
FIG. 4 is a right side elevational view thereof.
FIG. 5 is a left side elevational view thereof.
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a top plan view thereof.
The broken line object in FIG. 1, showing an outline of a human chest, is environmental and forms no part of my new design.