One of the easiest ways to give your old toilet a water-efficient upgrade is to divert the amount of water the tank holds and uses per flush. An old trick (that you should not do) was placing a brick in the tank; it filled up space and forced the toilet to flush with less water. The problem with using a brick is that it's made from baked clay; over time, water breaks down the brick, and particles and other sediment clog the plumbing. If you can't replace your old toilet with a new water-efficient one, fill a plastic tub with pebbles and seal it with a tight-fitting lid. Then place it inside the tank. You'll save around 2 to 3 gallons of water with each flush.