I'll bet you thought I was talking about your gas tank, huh? No, I'm referring to your toilet! "Old Folk Wisdom" says that you should place a brick in the water tank of your commode to conserve water. However, this could prove to be problematic as the brick will disintegrate over time, leaving particles that could damage your plumbing. My suggestion is to place an empty glass jar, without the lid, into the water tank. That way, when the water level rises, it will also fill the jar and keep it in place. A cautionary: make sure that the jar does not disturb any of the working parts.
The average toilet uses between 3 and 7 gallons of water per flush. By using the jar, you can potentially displace enough water to save up to 10 gallons of water per day (in a typical home).