Kreem is a product which seals/protects the liner of your gas tank.
From the Internet; "In a new or old tank, Kreem will seal and protect, prevent rust and stop leaks from pinholes and hairline cracks. Resistant to alcohol and gasohol; withstands most octane boosters. Most tanks require one pint of Kreem per three gallons of capacity."
- Note: While Kreem might have been the hot tip in 1975, it's likely or even plausible that a new product with a better makeup exists. While "Kreeming" your moped might have been wonderful 20 years ago, opening a tank on a bike you're looking at to buy and finding it was Kreemed in '84 isn't always the best selling point.....