Ocean|Tower Hints for iPhone/iPad
Also on: Android
Scroll down to the lower end of your tower and activate the submarine section on the left side but don't start the trip. Then scroll up to the top of your tower and start the trip.
After finishing your trip scroll down again and activate the submarine section again and the submarine waiting line is full again without any waiting time.
Don't forget to scroll up again before you start the trip again.
You can repeat this again and again and make money very easy.
