My neighbor is a HC sherrif, he said as long as the line is not hooked up to the bottle. It can be full, hooked up to your intake and all that, just don't have the line on the bottle. However if the bottle is in yor trunk, you need to give the cop permission to search your vehicle, or he has to have "reasonable cause" (open beer cans, liqour on your breath, weapons..........) to search your trunk.