Observe Beforehand
There is no dunk tank standardization, either in construction or rules of operation, so a number of factors may determine success when attempting to hit the target. If possible, observe someone else attempt the feat before you. Take note of the throwing distance and watch how sensitive the target mechanism seems to be. Considering these factors in advance will greatly increase your chances of hitting the target and dunking the person.
Balance Speed and Accuracy
The dunk tank is a fairly straightforward game: throw the ball and hit the target. The most important aspect is the throw. Many throwers try to hurl the ball with too much speed and little accuracy, while others take careful aim at the expense of the force necessary to trigger the target mechanism. You want to find the right balance in your throw. To increase accuracy, start with a stable stance, position the non-throwing shoulder toward the target, step with the same side foot in that exact direction, and point the non-throwing hand directly at the spot you want to hit. Increase or decrease the throwing speed until you are confident a successful throw will ensure a dunk.
Practice
Practice makes perfect. If you know in advance that you will be attempting to dunk someone, take the time to to practice throwing at a small target from various distances with different types of balls. Baseballs and softballs are common choices at a dunk tank, but any ball is technically fair game. Focus on throwing mechanics and experiment with different balances of speed and accuracy.
Focus On The Target
Block out distractions. The person sitting over the water does not want to get dunked. He is your competition and will likely attempt to distract you with funny outfits, comical gestures or taunting. People in the crowd may be adding the pressure. Do not pay attention to the activity around you and keep focused on the target. You will get the final statement when the person falls into the tank with a splash.