Although preparation for a Liver Flush is helpful, its not required;
Preparation involves using various products to soften or break the Gallstones so that it lowers the possibility of getting a stone stuck;
Apple juice, which contains malic acid is beneficiary if taken everyday for a week or more prior to the liver flush. Gold Coin Grass and Chinese Bitters also help softening the stones if taken everyday for a few weeks prior to the flush.
Chanca Piedra is also good as it helps breaks stones.
These are all part of the preparation; don't be discouraged if you can't find these or can't wait that long for a liver flush, go for it anyways with minimal or no preparation as the chances of getting stone stuck are minimal.
The essential part of the Liver Flush involves taking Epsom Salts (Magnesium Sulfate) to relax the bile ducts and aid bowel movement, and to take the olive oil and grapefruit mix to push the bile out, forcing the stones to come out.