The ornamental design for waterline cartridge, as shown and described.
FIG. 1 is a perspective view showing the design of the waterline cartridge.
FIG. 2 is an elevation view showing the design of a waterline cartridge.
FIG. 3 is another elevation view showing the design of a waterline cartridge.
FIG. 4 is another elevation view showing the design of the waterline cartridge.
FIG. 5 is yet another elevation view showing the design of the waterline cartridge.
FIG. 6 is a cross-sectional view of the design of the waterline cartridge taken along line 6—6 in FIG. 3.
FIG. 7 is a top view of the design of the waterline cartridge; and,
FIG. 8 is a bottom view of the waterline cartridge.
In the figures, the broken lines are not part of the claimed design but are necessary to show the environment related to the claimed design and to define the bounds of the claim.