sounds like your builder plumber has a cowboy hat, your building control office may well pick up on the joists drilled incorrectly and will con dem them, that means all the joist will need changing and the carcass will have to come out. the pipes in the floor screed all should be in plastic and...
i think the gas safe register, trading standards and local building control would find this install interesting. it could be run into the waste system below the sink.