seems to me like you have a few options. If i recall, a few other people have dealt with large stones, hopefully they will post some specifics for you. in addition to trying to flush them out, you can shrink them with things like chanca piedra extract, though it takes time. but hey, if you want to keep the gb, patience is in order. i too am curious whether anyone has flushed such a stone out... Andreas Moritz , with a forum here, says it can be done and some of his advisees have done so. and, if all else fails, surgery will always be there, but it doesn't work vice-versa.