Okay, no replies.
I haven't let this one go.
Been drawing up plans and searching everywhere.
Here is a possible answer.
It's a saltwater solution to my problem.
I don't know how I arrived at the idea of allowing the water to overflow.
I was thinking of using silicone to place a plexi devider into the display at a shorter height to allow water to feed the required piump...
The sump/refuge systems usually take water from *drilled* tanks, but I found Hang On Back systems for sale, which lead me to a DIY system.
http://canadafishtank.com/wp_marcel/...rium-overflow/
What do you folks think of this?
It seems the best way to get mass amounts of water out of the display tank without sucking everything else with the water.
All these salties on here, ya know...
Looking back on this question, I'm suprised that overflow boxes were not suggested.
I suppose everyone here is "Drill baby drill".