Trying to fit a new shower today, and hit a problem. Like most showers it has a couple of entry points for the water pipes. i have chosen the lower entry point,and the instructions tell me to remove the lower plug by pushing the collar up. try as i might this plug will just not come out ,although it seems to move up and down by about a quarter of an inch. i dont want to force it to much as i dunno what damage this may do. am i missing something or what? Any advice gratefully received.