We have three bathrooms in the new build, one with a bath, one with a shower tray and one with both a bath and a wetroom former tray (because we couldn't get a 900mm square tray to line up the waste with the joists). These rooms have all been tacked with green board and plastered so we're now looking at tanking and installing the showers so we can get on with tiling. So, given we have two different types of shower tray, what's the right order to tank? Tiler says put the former in,