You sump with a knob on the fuel selector and switch through the tanks. The fuel shoots out of a clear plastic hose on the plane belly. If you want to test it for water you need to position a bowl in the right spot. If you just sump onto concrete you look for water in the puddle. The tanks have bladders but I am not aware of any unusual problem with folds or wrinkles. The fuel caps are the thermos type but they are located underneath protective doors so they don't really get direct water exposure. The rust suggests that this was an ongoing problem. Did he have a fuel tank on his airport or did he ever refuel from drums?