I asked my uncle plumber... black pvc
is used for sewage disposal in homes so it does not have to be drinking safe... and plumbers NEVER use it for drinking water pipes. They only use the white pvc
. Something about the chemicles used when compressing the plastic pelets into the shapes.
I figure if a plumber won't use black for MY water supply, it isn't good enough for my fish! Instead I put aquarium sealant and pressed the substrate in firmly. After a couple of days to cure fully, a really good rinse, it was ready. Ready made cave for the fishies and camo'd.