In all the recent posts I have seen, no one actually drinks a second glass after they throw up- because there is still somne vomit in their throat and mouth people just can't get themselves to swallow this vomit because it's so gross- and it would just come right back up anyway. I think Stans Guide has a lot of tips that can help, of the people who posts what they are doing, I haven't seeen anyone say that they actually drank a second glass.
There are people who have posted here recentloy that they threw up after going unconscious and this ruined their attempt- this definitely does happen.
Sn by itself, without the regimen of other medications and fastnig in Stans Guide, seem s to result in vomiting and a failed attempt every time i have seen. The other medications are essential for it to work.