The best time to flush is 2-3 days befoer full moon. New moon is next to it.
Also flush results depend on many things
- if the flusher is weak and tired - less stones to none
- if big stone is blocking the way - very little stones until big one is broken and out
- it takes time for stones to move into "flushable" position
Finally, good flush could be done on any day, regardless of moon phase
Often I feel stones in my GB/liver, starting a few days before fool moon, but never before or on new one