They're referring to the Clark protocol, which says to make up a HUGE batch of Epsom Salt water (most use apple juice) and have two doses prior to the oil/juice, and two doses the following morning. Some of us like to forego the morning doses as unnecessary - we've got enema buckets or get colonics instead - and some of us, like me, don't take Es at all ever. We just dissolve our stones prior to the flush, or at most use magnesium citrate, a gentler form of magnesium.