I am in the process of finishing our basement and have already roughed in for a full bath and had it inspected by the local building department. We have also replaced the concrete but have left a dap out or "hole" approximately 12x12" where the tub drain and overflow assembly will connect to the drain. The question is whether the hole needs to be filled in and/or topped with concrete at any point in the installation process, or if it can just be filled with the gravel that came out of the hole in the first place. Is some form of concrete "cover" required by IRC or UPC?