What are the mechanics of a dunk tank?

Get a big plastic tank filled with water. You can use an industrial sized barrel, storage tank or some sort of above ground pool.

Take a large board, wide enough to fit across the tank, and cut out a rectangular piece from the middle for the seat.

Attach the seat back into the support board with heavy duty hinges at the back so that it can swing down freely.

Attach a heavy duty door latch of the type used in public restrooms to the underside of the seat so that, when the latch is closed, the seat can't swing down. Use screws and epoxy to attach and reinforce it.

Horizontally mount a bicycle wheel on the far side of the tank. It should be mounted on the same side that the latch is going to be on. Mount it in such a way that it will spin freely.

Create a target. You can use a simple piece of wood, a caricature, or anything else. The point is to make something for people to throw at.

Nail the target to the end of the lever arm.

Attach a large lever arm to the bicycle wheel. This is the board that the target is going to be mounted on, so it should reach out far to the side of the wheel.

Cover the seat board with something comfortable to sit on. This is going to be the seat, so you want to use something padded. Foam attached with contact cement would be an excellent choice, but even a thin layer of cloth or vinyl would work.

Attach the longer board across the top of the tank so that the other board swings downward when released. Depending on what the tank is made of, you could use epoxy, nails, brackets or any combination.

Attach a string from the bicycle wheel to the latch so that, when the lever arm swings back, the latch pulls out and releases the seat.

Fill the pool with water...

c because the action was the roller coaster reaches bottom of hill (action) reaction would be blood tends to drain away from head

hope this !