I think the question was how do I flush my system, not how do I get help with my drug problem. There are going to be many lame ass answers. If this is a test for probation or parole, then you are gong to be supervised and you will need to do a basic water flush. Reverse engineer from the time you have to test. Go back three hours and start drinking water. This process is going to take a couple of hours and you need to time things correctly. Don't drink to much to fast, it takes a few minutes to get your bladder working especially if you are still under the influence. Meth impedes you ability to pee. Drink a quart every 15 minutes. Three pints the first. Once you start peeing, you are going to need to be using the restroom every 10 or 15 minutes. After two hours, you should have gone 7-8 times. After you have gone 5 times, take a B Complex capsule which will give your urine some color. Before taking the capsule be sure your urine is completely clear. By the time you get there you will be peeing water but it is colored by the B Complex. Don't make yourself sick by drinking too much. Follow instructions because if you don't and wait to long, don't drink enough or wait too long from start to test, the poison will get back into you urine. This is not really good for but that does not seem to be a concern.
You won't be able to flush out right away, charcoal is best. Get help. Please. This will kill you