Sump circulation question

[bassman]

I have a 55 gal display with a 1.5" u-tube overflow. So I am not 100% sure just how much flow (drain) I am getting. I have my return throttled back a fair bit so I am running as fast as the u-tube will allow I guess. I am sure my drain can handle more. The overflow box drain is also 1.5 "

Maybe 800-1000 gph? I am having trouble figuring out how much water the u-tube will allow.

My sump is two jumbo rubbermaids connected together with one 3" pipe. see attachment.

The water surface is just moving in both sumps, a tad more in the sump where the water enters from the main tank but not much more.