Why hasen't this been in the game. It basically directs fluids into the front and overflows go from the sides...

Sorry, I don't really understand what you're suggesting.

Can I get some actual, full, descriptive, sentences instead of a rude demand of "why isn't this in the game"?

Oops, I didnt mean to be rude there, but i thought of an block that can simply bypass fluids into an overflow, like it goes to one direction, and if it is blocked, it transports to another direction.

We have valves and redstone control - you can make this yourself right now with a little bit of logic. For example, on a tank, you can take a comparator output from the tank using the Redstone Probe and apply it to a pipe valve with relatively minimal effort.