Pokemon Go - Secret Eevee Evolution Hack
This video will show you how to control the evolution of Eevee to make sure that you get the form you want. By renaming your Eevee before evolving it, you can ensure that you get a Jolteon, Vaporeon, or Flareon.
To get the specific form, name your Eevee the following names:
Flareon -- Pyro
Vaporeon -- Rainer
Jolteon -- Sparky
Make sure you capitalize the first letter of the name.
Also, to be safe, you should restart the pokemon go app after renaming your Eevee to ensure the name saved on the servers.
If you follow these steps, you will have a 100% success rate!