Koolance VLV-10TSPL Drain Valve for ID 10mm (3/8in) Inline drain valve to expedite coolant evacuation without turning your unit upside-down. Nickel-plated brass. To use, simply install the valve on a 10mm (3/8in), 13mm (1/2in) OD line near the bottom of your setup. When you need to empty the system, place a 1-Liter container below the valve and unscrew it. Next, open the top Koolance reservoir refill plug on your cooling system.