If you were able to drill the tank you could do what a lot of people are doing now with reef systems. You can put in a closed loop where you can suck from one end and have the return enter at the far end, and a few assist spots along the way to help move the current along. And you could use a large pump like a Hammerhead to pump 2500 gph to create the fast flow of the water. that way you only have 1 pump and have up to 4 pushing spots.