OK, here is an experiment to verify whether the flushing proceedure can produce fake stones or not.
I would do it myself, but I've just finished a flush, so I'm looking for a brave/enterprising volunteer.
Basically mix the Olive oil/Grape fruit concoction as normal and add some food colouring. Blue would be great, or red even. Basically a colour which is different from the usual tan/green/yellow that people find. The flush should proceed as normal.
Examine the contents of any stones you pass, noting the colour of the inside.
If the stones are fake, they should be the same colour as the food colouring added. If the stones are real they should be colours other than the colour added.
So, do we have any volunteers for this experiment? Preferably someone who is flushing tonight?