I´ve done my first two flushes using no Epsom Salt and they were succesful. Mrs Chang from Sensible Health says there´s no need to use Epsom Salt as it is heavy on the kidneys.
However, in my third flush I had to use Epsom Salt as I was in pain and my flush was fantastic.The pain faded after an hour.
Although I don´t think epsom Salt is a must I´d recommend it, according to my own experience.