

I don't understand the physics of solid lifting overflow piping.
For context, I have two fish tanks, A and B, and a filter tank. I have set up SLO piping from fish tank B to A, and from A to filter tank. The thing is, the SLO seems to flow strong/well from fish tank B to A. But it flows weakly from fish tank A to filter tank. The diagrams are approximate illustrations of my setup. Any idea why?