Atkins explains the liver/gallbladder flush in his book AGE-DEFYING DIET. Sounds hokey but here are the directions:

1) Mon thru Sat noon eat normally but try to drink as much lemon juice as your appetite permits - mixed with water (and sucralose if wanted)
2) eat normal lunch on Sat
3) 3 hours later, dissolve 2 teaspoons of sodium diphosphate (milk of magnesia) in 1 ounce of hot water and drink it
4) repeat step 3 two hours later
5) for Sat dinner have only fresh grapefruit, grapefruit juice, or other citrus fruit or juices
6) at bedtime have 4 ounces of unrefined olive oil followed by 4 iounces of lemon juice
7) immediately go to bed and lie on your right side with your right knee pulled up close to your chest - stay that way for 30 minutes, then go to sleep
8) next morning, before breakfast, take 2 more teaspoons of milk of magnesia dissolved in 2 ounces of hot water. From now on continue with your regualr diet

He says the liver flush has a relaxing effect on you bowels (well, duh!) and that you may have irregularly shaped light-green objects in your stool the next day. This is normal he says.