The amended flush you discussing is the flush i now regulerly use. Think i started using it after my 3rd flush. for the second drink I use the same amount of grapefruit/OO mixture as the first drink the night before, (not 1/2 a cup/dose). works fine for me.
Since you have already opened the bile ducts the evening before, the second drink is more of a "straight through" kinda experience. The reason i started doing this is because i was slow to get stones, first and second flush only produced 50 stones in total. sometimes i lie down for 20-30 mins after, then have a BM. sometimes i don't & it's really is quick, litrally BM straight through.