My tank is 4by 16 by 36. I ran a 20 inch overflow on back of tank (outside not inside) had 1 inch deep by .5 inch wide grooves routed every inch. Put in two 1.5 inch overflow pipes inside box. Two 1 inch returns one on each end of box. The overflow drains into two separate socks. One with carbon and one with puritan. I teed the two returns into one and connected it to the return pump. I also ran a pipe for chiller and two for a gfo and bio pellet reactor. The return pump is rated 2200 gph