Cat box, bag it and toss it, find a playground sand box, just don’t put it on the beach or in the ocean, let it dry out in the sun or bury it in a landfill.It was always my intent to use chlor-out after thorough rinsing the rock. I also will run high end carbon for some time before adding fish while using turbo 900. I’m optimistic after first rinse as the detergent suds really dissipated rapidly. My guess is that the concentration of detergent must have been rather low.
So I now have rinsed with and drained again. Next step will be to remove the leftover rock and all the sand (don't know where to dispose the sand?).