The system consisted of a combination of slotted and un-slotted coils of AG pipes on the bottom of the tank.The slotted and un-slotted pipes were coiled in parallel, but with each starting from the opposite side of the tank.The two coils were joined in the middle of the tank by a central polyvinyl chloride (PVC) joiner. On the two sides of the tank, the slotted pipe was connected to a “pusher” standpipe, and the un-slotted coil to a puller standpipe.