ABWA

6. Variable height lock-in floor grate:

A unique waterproofing system used to seal the tray to the drain. (page 27, "The Bathroom Book") The inner floor waste is free to move to any height required for the tilers to cement the tiling bed, whilst still ensuring a complete waterproof seal. Sealed with neoprene washer (Sydney Harbour Tunnel sections are sealed with neoprene, and are expected to give a waterproof seal for at least 150 years. Source: Transfield Subemo Australia, constructors of the tunnel.)