1996 Toyota Camry Gasoline additive

Hi there! I bought a concentrated fuel injector cleaner that says I should add entire bottle to nearly empty gasoline tank, then fill tank with up to 21 gallons of gas (my tank is around 16 gallons). For best results, it says, do not refill tank until near empty. Then it says to do this every 3000 miles. It is called Gumout and it is suppose to clean fuel injectors, prevent future deposit build up and restore lost horsepower. Is this a good idea to do? Is this a waste of money? Will this hurt the engine? Should I do it every 3000 miles? Thanks. Michaele