How does a diuretic pill reduce blood pressure??

How does expelling urine after taking a diuretic pill reduce blood pressure? I understand when a submarine dives to lower depths, the pressure on the hull of the sub increases due to the weight of water acting on the hull of the submarine at deeper depths. What is the mechanism of expelling "water" leads to reduced blood pressure?

I suggest trying to lower your blood pressure through a diet change and naturally. They expect you to stay on those pills all your life, which if you start taking them, you will have to be. When you're on certain medications long enough, your body adjusts to them, and begins to rely on them. If you lower it naturally, you may never have to take those pills again your whole life (if you keep a proper diet and such).