The ornamental design for a single scubatankadaptor, as shown and described.
FIG. 1 is a rear perspective view of a single scuba tank adaptor embodying my new design attached to a scuba tank backplate, wherein the scuba tank backplate, single tank and tank holding harness are shown in broken lines for illustrative purposes only and form no part of the claimed design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a side view thereof, the opposite side being a mirror image thereof;
FIG. 5 is a front view thereof; and,
FIG. 6 is a top view thereof, the bottom being a mirror image thereof.