Diuretics are be good for pulling water fast, but they can also be dangerous. If you want to use one in conjunction with a water manipulation plan, a diuretic will get you looking tighter/drier for a day. So if you want to look good on the beach, with a little prep 1 wk out, you can use a diuretic in the last day or so. Just remember that the fluid you effect will come right back, especially if you eat high sodium. You don't want to get into the vicious cycle of adding more diuretic to combate the continual water that will then be retained after. Diuretics can cause kidney damage in a short time. 

You'd be better off doing a lot of this work the old fashion way. Get lean. Thats the first part. Get very lean. Thats the second part. Then use an Ai to reduce estorgen to dry you out more. Add in some Winstrol oral for a few wks and will push water out