Lu Blue cleans and freshens your toilet with every flush, whilst turning the water a pleasant blue colour. Features & Benefits PDCB and phosphrate free. Contains a pleasant perfume. How to Use Remove the toilet cistern cover. Lift tab on the card and pull back. Do not remove the wrapper on the block as this will dissolve in the water. Drop the block into the water opposite the water inlet. when the colour begins to fade, replace with a new block.