A machine that will conditionally sort products that move through it. I imagine it would be a speed-1, 1-tile machine with no operation cost (since it’s not actually changing the drug). The condition of the switch could be anything, although concentration seems like the most obvious approach. If the concentration is above a user-set level, it outputs on the left, otherwise it outputs to the right.
Such a machine would allow for complicated, condensed lines if used carefully. It could also make for more efficient uses of fast machines as part of multiple slow lines.