I put the colander IN the toilet. Shake the colander and flush the toilet a few times and all you will have left in the colander are stones. If I want to save the stones I put them in an empty baby food jar, stored in the freezer. In between toilet visits the colander can be hidden in a bag. At the end of the flush I pour bleach in to toilet, on top of the colander and scrub it with the toilet brush.