Diuretic use is largely contingent on the shape you're in. Lets assume that you're ready, everything is tight and you just need to shrink wrap the skin..
Now the question is, did you salt your food during your prep? If so, you should be drinking 1.5 gallons of fluid per day already. In this instance, the week before you push double, even up to 3.5 gallons per day and continue to salt food (sea salt or kosher mineral salt, every other meal, lightly).
Assuming the show is Saturday, you'll have to make a judgement call on when to cut water. Personally I circuit train and carb deplete up til Wed, then thurs start slowly introducing carbs. Thursday night I cut water and drink one gallon or less Friday up til noon while continuing carb up.
I will continue to lightly salt food, water is gone, carbs coming in. IF NEEDED Friday night I would take a dayside tab and maybe one Saturday morning. Should be all you need.
Lasix and other potassium wasting diuretics are more complicated.
In all, if you don't understand cause and effect with diet and cardio, you will be in the dark employing diuretics.
