The bath waste is the 40mm going into the 50mm above floor level, thus no good for the shower waste. The lower 40mm is the old header tank overflow, which theoretically could have been used for the shower waste, the far end of it however stopped 30 feet away near the ouside wall, ie it went nowhere; and it was full of water. Bit odd. The 50mm pipe joins the 110mm soil pipe, seen disappearing in the same direction, although thankfully that did go somewhere.