Please don't put urine in the jar! That is just gross and it is not a fair representation of what you are doing to your body.
By all means put water in if you want - the body is mostly water. I can't honestly remember if I put water in mine. Maybe start out dry and then add water if necessary.
This isn't about tricking you into giving up smoking. It isn't even about grossing you out. It is about you seeing the truth of what you are doing to your body each and every day.
BTW I don't condone chain-smoking. It can be dangerous. It certainly felt dangerous to me when I did it. But you need to get beyond the point of satiation - until you've well and truly had enough. The problem with smokers is that they never get to this point. They always stop before that level. So the last cigarette they have is always a pleasurable one. You want to get to the point that when you have your last cigarette you never want to see another cigarette again in your life. That's when giving up will be easy.