I've done 11 or so flushes and never once used HCI. The important parts are increased water intake (especially on flush day and the day after), the magnesium (usually Epsom Salts , but magnesium citrate appears to get good reviews as well) and the oil/grapefruit juice mix.
I also drink fresh, unsweetened 'raw' apple juice for a few days before a flush because Andreas and others recommend the malic acid. Also, I usually do a 'salt water flush' the morning of the Liver Flush to help clear a path through my colon.
Salt Water Flush
* A full quart of luke-warm water
* Two level (rounded for the Canadian quart) teaspoons of Sea Salt
Just stir the salt into the warm water.
Do NOT use ordinary iodized salt as it will not work properly.
First thing in the morning, before eating or drinking ANYTHING, drink the entire quart of salt water. (It helps me to 'think' of it as heavily salted chicken broth.) The salt water has the same specific gravity as the blood, so the blood won't pick up the salt and the kidneys can't pick up the water. Expect to have a few rather urgent bowel movements within an hour of drinking.
If the salt water does not work the first time, try adjusting the amount of salt a little up or down until you find the right balance.