Sorry will not happen, the top of the fuel tube on some cars maybe plastic but it turns into steel way before the flap, good luck cutting that. I guess you guys are going to sit there cutting with a manual saw through the side of the fender. Yeah and also people are going to be bugging out with a 1990s or earlier car??? I have not seen to many Ford LTDs or AMC Gremlins running down the road. Good luck. Besides the smart guy that is in a pickle would have used a punch to pearce the plastic bladder around the tank then the tank itself. Cut the fuel line running along the frame may also help. I guess the point is gas pumps will be dry by the time you need to fill up..along with all the other cars on the road that ran out of gas waiting in backed up traffic.
Then a siphon for water??? Where would you need to do that???? Are you going to siphon water out of toilets. If you are, take a cup of bleach with you. 15 drops of bleach per gallon of water, let sit for 15 minutes, that will kill any bacteria and will make the water "safe" to drink bacteria wise.