I am a newbie in water system design but I am currently faced with the exact situation below on my land, and I need to know whether gravity alone is sufficient in order to fill Tank 2 from Tank 1, as I already experienced backflow.

Please have a look at this image:

![enter image description here](https://i.stack.imgur.com/UNgGu.png "My current water system situation")

*Note: let's not worry about how Tank 1 is being filled as it probably does not matter - I just made sure I never used a pipe diameter smaller than 0.5" between Tank 1 and Tank 2.*

As you can see:

* My water source is the overflow of Tank 1
* I have put a 1" diameter pipe in the first 'downhill' section of my path
* The second, longest section of the path is a pipe of 0.5" diameter
* The system is 'powered' through gravity alone

**Questions**

* Is there any missing variable (eg path length?) on my drawing in order to resolve this system? (What are the important variables?)
* The flow at the source (the overflow of Tank 1) can be nearly 0. How does this variable influence the system? (Can a larger flow at the source help going up the 'uphill' sections between the tanks?)
* Is the 'head' variable important at all?
* I used a bigger pipe for the first section in an attempt to 'make more weight' and create sufficient pressure to go up the small uphill that follows. Should I limit the use of that bigger pipe strictly to the downhill section, and does it actually make sense to have used a bigger pipe at all?