almost every stimulant is diuretic, if you only drink coffee and tea you'll shed some pounds fast, BUT only do this the day before and the day of the weigh-in. shedding water weight to early will stunt your total weight loss progress.
NOW LISTEN UP AND LISTEN GOOD:
this is what I did once, along with a couple of hours in a sauna and half a can of copenhagen, to shed some serious pounds pretty fast. I DO NOT RECOMEND THIS AS IT CAN KILL YOU. But I was young, dumb, and out of my weight class. AND my meet sucked because I was so crapped out. I do not recomend doing this program to a tee, but use what knowledge you can gleam from this, and don't freakin' die. I'm serious.
a week before your final weigh-in mix a bullion cube and a teaspoon of epson salt in a glass of water and drink (epson salt has a slight laxative effect so use no more than a teaspoon, and don't drink this if you have plans for the next hour, just to be safe,) do this for the next four days, drink as much water as possible, and put salt on everything. this will cause your body to become used to ingesting alot of sodium and water, and you'll bloat up like a balloon, but exersize will become easier (I don't know how much easier cardio would become, cause I only lifted when I did this). then for the three days up to the weigh-in cut almost all sodium out of your diet, and drink a little less water than you're used to. one day out drink only coffee, take a good b vitamin complex (some b vitamins have a diuretic effect) and any diuretics you want (be careful though, seeing as massive amounts of diuretics can FREAKING KILL YOU.) and the night before the big weigh-in, four hours before you plan on going to sleep, mix two tablespoons (NOT teaspoons this time) of epsom salt onto a glass of water (which tastes like rotten ass,) get a newspaper and spend the next few hours on the crapper. wake up, eat nothing, sip a little coffee to keep your mouth wet, and win this thing. revel in your success, then eat and drink, if you are still alive. And the final step I took was to make a solem vow to never try to shed that much water ever again.
hope this helps, and I'm out.