The ornamental design for a portabletoilet, as shown and described.
FIG. 1 is a perspective view of a portable toilet showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a side view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The broken line showing of bottom details in FIG. 6 is included for the purpose of illustrating portions of the portable toilet and forms no part of the claimed design.