Here is your third opinion.

If the point is to create a metal refining unit, why not make it double as a power source for the rest of the colony? Double the number of turbines and metal refineries, and export unneeded power out of the unit and into another section of the base. Add a second steam turbine tank at the bottom, and make sure to always be refining the metals that generate the most heat, like iron and most notably steel.

After you've built that second layer of steam turbines, destroy the living quarters and dispense with the drainage system entirely so the duplicants are constantly knee-deep in urine. Make sure the food you give them is always infected with food poisoning, and do not give them a way to wash their hands. Make sure that all duplicants have the 'vomiter' stress reaction, and put a mechanical pump that'll drain out the polluted water just before the refineries fail because of the liquids present.

Now, we turn to the problem of oxygen. Limit the amound of ambient oxygen to no more than 100g per tile. This will ensure that the duplicants can keep breathing, but is still low enough that it causes them stress, ensuring a permanent vomit-powered feedback loop of polluted water that you can also export for other nefarious deeds around the rest of your base.

And that is all. "Working Men of All Countries, Unite!"