I am not looking for permanent weight loss, only for a weigh in.

Wrestles, boxer, mma guys are notorious for fast weight loss. Here are some of the things that they do to lose weight quickly, but let me remind you that it's not healthy at all.
Before performing the below, you should consume plenty of water since it will help speed up metabolism and get rid of unwanted cellular waste. The stuff below should be done either the day before or a couple of days before.
Sauna: Perform sets of 25 minutes in them (the more layers you wear the faster) depending on how much you need to lose.
Running: Perform fat burner/ hill mode on the treadmill and run with as much layers on as possible.
Spitting: Throughout the day, spit in an empty coke can or cup.
Sodium free: The less salt you consume, the less water is kept in your body since sodium holds it.
Diuretics/Laxatives: They both cause a drop in water level and laxatives can help get rid of left overs in you large intestine.
Colon Cleansing: Get you colon flushed out. It ain't pretty, but you can actually lose 2 pounds from this depending on your diet beforehand.
At weigh ins: drop as much clothing as possible.
P.S. after losing at least 3% of water in your body, you'll have a significant decrease in performance. It also takes about 24 hours before you can fully rehydrate and regain lost performance. So do the math and if you have to lose more than 3% water weight, then your better off competing in the class above your target.

Drink tons of water.

Trust me you do not want to go through what a boxer does to lose weight fast. My friend is an amateur boxer and usually a tool they use is a 4hr workout (skipping, jogging, cycle, sprint)in a polyester tracksuit (heat body up) and a lot of sauna. keep in mind that all they are dropping is 80%fluid, you put that back on when you shower, drink and eat. so its very temp.
http://myfitmate.blogspot.com/

i used to box and if you want to lose weight like i used to you have to be on a strict diet run about 5-6 miles a day jump rope 30 minutes and if you have heavy bag hit it with all you got for 30 minutes rest in between ok

they out on a lot of layers and do an intense workout, sometimes for several hours, up until they way in. you sweat alot of water out that way. some also spit which doesnt help that much