Dear Customer,
The lower drain has a stop valve, when you open it, the coolant won't start leaking until you screw in the soft tubing fitting and soft tubing. Such as our fitting BP-WTP-C02 and soft tubing BP-PVCT3858CL-2M.
It is hard to get all the coolant out unless you disassemble each part of the system.
Or you can turn on the pump, one side fills in the distilled water on the top, and the other side drains the coolant from the bottom.
If you have any questions, feel free to contact us.
https://shop.bitspower.com/index.php?route=product/product&product_id=2246&search=C02&page=2
https://shop.bitspower.com/index.php?route=product/product&product_id=2898&search=3858