Fluid combiner and Water pumps.

[Kittentheboss]

So i have a fluid combiner hooked up to pumps on all 4 connections of it. i have the fluid combiner input connected to the tree pumps that are connected to the 3 water pumps. the output (36) is connected to a pump distributing water on my crops. The issue is the 3 water pumps in the river. 2 of them on the left are completely full. the one on the right seems to be draining faster. I though a setup like this would EVENLY distribute the water from all 3. Not drain 1 at a time and keep the 2 full. Is this issue fixed? Am i doing it wrong?