Please look at my layout and suggest a good location for a loop drain and hardware to use.
I will add the drain port in about 2 weeks when I WC my video card a EVGA GTX 670 SC 4gig(short 670) with an XSPC block
I have never liked the idea of a drain line for a closed loop system it makes it harder than it has to be try using a fill/flush system added to the loop, something like this. It allows you to direct the flow of water through a makeshift reservoir, but this is how I do things you may have a better idea. This idea will work anywhere but It works best if placed right before the pumps inlet.