The ornamental design for a petdrinkingfountain, as shown and described.
FIG. 1 is a perspective view of a pet drinking fountain showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof;
FIG. 9 is an enlarged detail view of portion 9 show in FIG. 1; and,
FIG. 10 is an enlarged detail view of portion 10 show in FIG. 2.
The drawings show broken lines in the drawings depict portions of the pet drinking fountain. FIGS. 1, 2, 9 and 10 show broken lines that represent the boundaries and indicators of the enlarged detail views. The broken lines form no part of the claimed design.