Harpic Toilet Rim block is a detergent block that comes with a Lavender Fragrance, which not only keeps your toilet clean and fresh, it also leaves a mild smell of lavender. Harpic Lavender Toilet Rim Block used in flush toilets gets dissolves in water slowly. They are usually placed in a small holder (such as a Rim Cage) that is placed over the rim of a toilet and hangs down into the bowl. The water passes through the holder coming into contact with the block as the toilet gets flushed. These may also contain a coloring, which shows up in the water.