Just pour in some dish soap and they will sink like a rock!
Absolutely correct!!! They are held "on top" of the water because of surface tension. Any surfactant will destroy the surface tension (that is why soap makes water work to remove dirt). Use one of the liquid detergents in a squirt bottle if they are close. But If they are farther away, throw a Cascade "pillow" (like you put in the dishwasher) at them it will dissolve with the moisture , the surface tension is gone and the drown.