The olive oil lubricates the stones so they come out but you can use lots of different oils for this purpose not just olive oil - safflower and almond oil could be used too.
The grapefruit just makes the oil go down better as in taste. I have never used grapefruit but instead use lemons.
What we get out is definately gallstones. I was once sceptic but after a lot of research what I am passing is stones. I during stages of a lot of cleansing have passed stones without olive oil or grapefruit/lemons. I get different types of stones but usually the one type each flush. I started which small green ones, moved to big green ones and am now flushing small and big yellow ones.
After flushes my metabolism appears to work better and I am relived from chronic shoulder pain in my right shoulder that I get. I definately think flushes are worthwhile.