I had originally thought that P4 was the limit due to needing a free cycle for handoffs, but realized it could be lowered to P3 by dragging the entire product. This moved the issue to waste handling, with my original plan being a giant track running off to the farlands as a peudo-waste chain, but realized that since Purification consumed atoms it could be used to free up grabbers and compact the waste, letting me make more compact (for a certain definition of compact) solution.