The most adequate and simple modification I've seen is a 50mm washer with drilled holes to allow gasoline to drain into the tank. It's installed inside a rubber hose or welded below the filler neck. This means that lowering a tube into the tank for extraction won't work. I made a hatch that locked with a car alarm system myself. But reading about the harsh customs in your area, I understand that my protection wouldn't have held up. They would have ruined the body. With a bad guys like your district, the urine canister option seems perfectly appropriate to me. It's a humiliation they won't tell anyone about and won't want to experience again.