I claim the ornamental design for a portable urinal, as shown and described.
FIG. 1 is a perspective view of a portable urinal, showing my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a left-side elevational view thereof, the right-side elevational view being a mirror image thereof;
FIG. 5 is a front elevational view thereof; and,
FIG. 6 is a rear elevational view thereof.
The broken line showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.