Find a partner to make this easier. You will need three controllers in total. One will play as a dummy Survivor and the other two players will need to be Infected. Whoever wants to earn this achievement needs to spawn as the Spitter, so keep spawning and cycling through the Infected until you become the Spitter. The other player needs to spawn as the Smoker.
Once you have used your dummy account to get the correct combination of Infected have your partner grab the Survivor with his tongue. Once the Survivor is struggling, fire a spit ball at the floor under the Survivor.
This achievement will only unlock for the person playing as the Spitter. This may seem a little tedious but it's the easiest way to do this without much hassle.
See "LONG DISTANCE CARRIER".