I have a 2' wide by 2' high by 12' long waterfall planter box constructed out of cinder block and stone veneer. Anyone have any ideas on what goes inside the planter box besides the pvc pipes ?? The sheer descents are installed as well. I was just curious if you are supposed to fill this entire box up with dirt ??? That's a lot of dirt LOL. I really though some sort of shelf was installed inside the box perhaps a foot below the top ?? This way I would only have to fill the upper half of the box. Thanks.