What is different with the tank than the bowl? Have you tested the water in both to compare the parameters? I doubt it is scientifically a preference for dollar store dishware and more likely something in the tank that is incompatible with their ability to live.
I’m going to guess something in your tank is from another tank that saw a copper treatment. Slow copper leeching into the water column will kill your inverts.
HappyHomework5643 
What is different with the tank than the bowl? Have you tested the water in both to compare the parameters? I doubt it is scientifically a preference for dollar store dishware and more likely something in the tank that is incompatible with their ability to live.
So your going to tell me you were going to flush two alive shrimp down the toilet?
was your tank cycled?
I’m going to guess something in your tank is from another tank that saw a copper treatment. Slow copper leeching into the water column will kill your inverts.
What is “regular aquarium substrate”?
if you need to euthanize please look up clove oil