A. The are called No Caulk drains because they will fit over drain piping and are sealed by an internal compression ring. Before modern plumbing technology came along, drains would have had to be caulked with lead and oakum to seal the drain to the pipe. Since the lead and oakum process has been eliminated they are referred to as no caulk. You will still need to use some type of caulking to seal the flange of the shower drain to the shower pan.