@Dancelot
Brother, you'll get down easy. I've had to do this a few times before, and also for 3 years when I used to row.
Ideally you don't want to drop weight 2 days out (your body won't be 100%, but i'll tell you how to get as close as poss to it at the end of this), but thats the situation you're in so we'll deal with it.
Like someone said earlier - its all about fluid intake.
Don't stave yourself, you'll still hold water weight, and energy levels will be zapped.
Whens the comp? Sat? do you no how much you lose overnight (ie, weigh yourself just b4 bed, and weigh urself first thing in the morning after taking a leak). this could be anything from 500g to 3kgs. Test it tonight (ideally you'd do it over a week and find an average), but that number will be what you have to play with.
Then you'll cut fluids starting tomorow arvo (if teh comp is sat)
Eat a normal breakfast, and around lunch time weigh yourself again, say your're 85kgs and u loose 800g over night, you'll only have to drop 1.2kgs. Which will be of water; and easy to do!
So for the rest of the arvo pretty much eliminate fluids. Maybe a sip here and there, depending on your weight in the evening you may be able to have a small glass. But cut it all out if you have to.
Eat a standard meal at dinner - you can play around with carbs (as carbs retain water in the muscle cells/liver) BUT you're close enough to 83 that you shouldn't need to do this. Just no fluids, or saucy/oily/watery foods (lol don't have soup)
The lack of fluids, plus the lost weight over night, should drop that 2kgs.
Then you want to get to the weigh in venue as early as poss - so you can be the first to weigh in.
If you can bear it, or if its possible (time wise) go weigh in and then come back to feed/rehrydate.
If thats not possible, then depending on your weight and how you feel in the morning, you may be able to have a small feed - think calorie dense (anything from sum nuts, to a mini shake with coconut cream, whey, and creatine - if you're worried don't take in any carbs at this time) but it must be small (weight wise). Have a multivit, and have some no-doz (caffeine) to help wake you up and suppress the hunger pangs (especially if u usually rely on breakfast). Take a piss, and sh1t. Do it again once you get to the venue.
I reckon if you do all this, worst case you'll be 200g over (strip to bare essentials). and if you've got there early, you'll have anything from 60-120mins to reweigh (find out). so just force it out in the toilet!!
THEN, as soon as you've made weight you need to eat and refuel.
You may have to start warming up in less than 60mins (once again, find out, prepare), so find something you'll be able to stomach. Ie, don't eat a fried breaky if you no it'll sit in your gut all day!! Just include some simple carbs. This is a personal thing, i no i'm good with oats and milk and can lift 20mins later. my mate would spew it all up on the other hand.
BUT, def down about a litre of water (you'll want it) with a powerade or even better 2 cans of coconut water (health shop - natures isotonic drink!)
but then remember that will need to be digested, so you don't want to be bloated. And make sure you have some plain water and not all sports drinks. Powerade is a tad too sugary and salty (electrolytes) so you body actually has to dilute it in the gut - you don't want this as you don't have the spare water. So drink plain water with it.
Then sit. Do minimal moving until you have to - if you're walking, blood that could be used by the stomach/intestines/liver etc to assist in digestion is being diverted to the leg muscles instead. thats why time is the critical factor.
oh, and stay out of the sun, don't get hot (you don't want to be sweating - until warmup time anyway)
keep sipping fluids throughout the day (you may not be fully rehydrated until bench or even deadlift time). try get your piss clear.
Take more caffeine as well, i've read studies that say you need ALOT of caffeine in the system to cause a diuretic effect so don't let that worry you.
then go smash some PB's!!
JUST STAY AWAY FROM A SAUNA! you will lose to much and will feel like shit all day.