To Flush or not to Flush ...

Depending on health issues, I would ask a health professional before detoxing, try a chiroprator, nutritionist, or naturalpath.
There are some organic and natural ways to flush your system. One chiroprator suggested natural, organic, unsweetened apple juice. Mix with filtered water and sip all day long for a couple days. There are teas and natural supplements as well, try the Puritan's Pride website and seach "detox", you might find some ideas there.
In the past when I have detoxed, I would do one day of clear liquid; water, tea, natural clear juices. Then the next day I would add some fresh whole foods, lettuce, celery, apples and keep up with lots of clear fluids, over the next few days I would slowly add in more foods, but try to avoid dairy and processed or unnatural foods. I have used supplements as well during a detox.
Unfortunately I usually slipped back into regular eating shortly after with packaged foods, meats, cheeses, etc. But a week of cleanse must have helped detox me a little right?

Your body is an efficient machine. Your kidneys and liver are there to help eliminate the "toxins". Lots and lots of water and fresh fresh food will make you feel better. Most "detox" plans are actually to help level off cravings for sugar etc. If you stick to a largely vegetarian diet for about 10 days you will feel better, your skin will look better and you will have energy. You can "flush" your system with out costly diet products, water is your best friend to loose and keep weight off.

Water is 100% natural and your body will work with it.

Plus, it's a lot cheaper than those Detox thingys you can buy!