The ornamental design for portable toilets, as shown and described.
1. Portable toilet
1.1 : Perspective
1.2 : Front
1.3 : Right
1.4 : Top
1.5 : Cross-sectional
FIG. 1.5 is a cross-sectional view of the design sectioned vertically as per the sectional plane and arrows shown in FIG. 1.2; the parts shown by means of broken lines in FIG. 1.1 are for environmental purposes only, and form no part of the claimed design.