I had a toilet installed by a plumber. It leaked and damaged the living room ceiling below. At least, I think that is what caused the damage. When I wanted to find why the ceiling was damp, I called a different plumber to check for leaks in the bathroom. He told me the toilet was improperly installed. The first plumber had used the rubber gaskets instead of a wax seal. Not only that, he had stacked two seals in order to compensate for the distance between the flange and the bowl.
The second plumber says you shouldn't stack these seals. The first plumber says you can. Who is right, and is there a plumbing code or book of best practices I can turn to to press the first plumber to accept responsibility?