Hey Anna~~
I think there's a thread somewhere in this website that teaches you how.
You might want to look around. I just typed in flush and it gave me a whole lot.
You said that's it's recommended for long fasts.
My question to you would be, Should I do one because I am going to do a 10-15 days fast. I have not yet decided whether or not to go the 15.
Please let me know and in the mean time I will be looking for that thread for you.