The 5000 ml Erlenmeyer Flask is the ideal vessel to make a large yeast starter for 10+ gallon lagers and high gravity brews. The best brewers make large yeast starters to get their beer fermenting fast. Large populations of active yeast help ensure flavorful beer free of off flavors. Because it is made from borosilicate glass you can move it from a boil on your gas stove into a cold water bath for cooling, without the risk of cracking. (Not recommended to use with an electric element.) This means you can do the whole process in one container, keeping it simple and helping to reduce the risk of contamination when transferring from one container to another.
For your safety, it is recommended to use to the double boiler method. This process involves using a boiling water bath on the outside of the flask to heat up the water inside the flask. All you need is a kettle that is 3 gallons or larger. This process is much safer and more efficient. If the flask should break or boil over, your kettle will be there to collect the contents, thus keeping your stove clean and keeping you away from potential harm.