Agreed. It should not be possible for it to siphon back to the wing tanks.
Check under the engine area for dye stains (if you had avgas in the plane). I've had one tank leak empty through the carb. Some people have this as a chronic problem if they don't shut the header tank fuel valve under the instrument panel right in front of the pilot. If you decide to just shut off the fuel valve, be ABSOLUTELY, ABSOLUTELY SURE YOU TURN THAT VALVE ON DURING PREFLIGHT. I had it listed in two places on my preflight checklist (which I used slowly and carefully every time) even though I didn't shut off that fuel valve. I recommend actually fixing the problem. Actual mechanical experts will tell you what needs to be addressed in the carb or other potential leak locations. Ed
