You could put the inputs for the closed loop in the oveflow you just have to worry about a couple of things. One is that you would have to make sure that no bubbles near it, perhaps a standpipe will keep the water spilling over the overflow to just the very top and then draw water from the lower reaches (tight plumbing though)
The second thing to watch for would be, would the overflow box be able to draw into itself enough water to accomidate all the pumps that are going to be drawing from it. I would do an experiment prior to drilling.
Mike
The second thing to watch for would be, would the overflow box be able to draw into itself enough water to accomidate all the pumps that are going to be drawing from it. I would do an experiment prior to drilling.
Mike