Here is the Chart













As you can see, simple pipes are the best way to transfer fuel but with any obstructions, it quickly loses flow rate. Furthermore, you can see that pistons are actually better than ropes when it comes to transferring fuel to another craft (via connectors) which I found odd since in every other situatio; the ropes did better.

How did I calculate this?
I used this contraption which transferred fuel from one tank to the other. When it reached 5000L the light above the tank would light up.










Then I used this logic to calculate how long it took for it to reach 5000L in seconds
and after that I would divide 5000 by the amount of seconds it took to reach 5000 to get my fuel flow rate in L/s







I hope you found this helpful, hav fun building!