We are in the process of replacing an all tile shower. The plumber has brought over a new drain kit which is cast iron. The drain in the concrete floor is pvc. And our tile man is concerned about a secure seal since they are two types of material. He is trying to prevent any future leakage which would settle under the shower pan should there be a back-up. Any advice? KD

Your tile-man is correct: if you have PVC pipes in the ground - than use PVC trap. But, it is perfectly OK to use Cast Iron shower drain that mounts over PVC riser.