this would be the easiest way in my opinion. you could drill each tank and plumb them all together and use 1 sump. would be a easier way to control the flow of each section
+1 on a drill press if you go that route. This is a cool idea man! The only thing I may suggest is that you leave 1/2 from the top of the water line so that all that film will go down the overflow. And maybe 1/2 inch from the bottum do that things in the sand may move around?