Yeah, you use that stuff to dissolve bodies.
I’ve cleaned a pool much of my life and muriatic acid is commonly used. HOWEVER not in the volume that they had; for the size pool they have, they might AT MOST use 1/4 gallon a week. They might have 1 or 2 cases of 4 - 1 gallon jugs. But they reportedly had 4-5 50 gallon drums! And were pouring down the drain? uh no ;(