Forget the inline thing and the sack of balls you're supposed to put in the tank - they so absolutely nothing. The manufacturers claim all sorts but it's all a con. I don't bother with liquid additive either, I know of a couple of people who have used it meticulously only to have serious valve and seat problems and many who have used none and have had no problems. Lots of people swear by it but unless you are doing high mileage or towing a caravan I wouldn't bother.