ANSWER:

Allah didnt tell people to go into such small details that are not even logical!

Are you going to use colored water with dye in it to see where it reaches and where it doesn’t?

What kind of Extremism is this? Simply put water in your mouth, turn it left and right and spit it! You don’t need to be a rocket scientist to understand this! However, when you give Satan room to mess with your mind, this is what happens. 

My question is, is it compulsory to reach water in all area of mouth in wudhu during fasting?when water reach in soft palate i feel doubt that water enter into neck. if i avoid water to reach in soft palate or posterior part of mouth during fasting, will it be okay??can i just wash anterior part of mouth?