Jim,
Thanks for that explanation. Did you see the photo of Paul's sump tank? Don't you think it was mounted too high? I bet yours is lower.

Jim S. wrote:

I don't have a Rutan type selector valve.  I have strakes gravity feeding the 5-gal sump through lines about a foot long.  Assymmetric transfer was such a problem that I installed electric
valves to DE-select (close off flow from) the tank that was transferring too much and let the other catch up.