look at some anatomical and physiological info, shall we?.  The glands that produce vaginal fluids are many and do not have large storage capability nor do they empty into a common duct nor can they produce that much liquid that quickly.  Sort of like sweat, tears, and saliva.  Therefore the gross volume must come from a stored accumulation. Even the male ejaculate can't contain that much volume and the male system is designed to expell volume with some force.  It seems to me that it must come from the urinary bladder.  Loss of bladder control is not too uncommon when there is a parasympathetic rush.