derpmaster :
Or off the sli block could i just include my drain?thereby ensuring it as the lowest point in the system
Of course you could do that, but as for myself I wouldn't!
Because it could and probably would be a place for a trapped air pocket and that you do not want.
And no matter where you put that drain line the possibility of draining the entire loop is very slim, depending on radiator setups they can still be holding coolant.
You can always flip the machine over and over to manipulate the water to the drain, if you have plenty of time and are going to make a days job of it.
But for me a line cut here and a line cut there and the coolant is out.
I never use a drain port, if I need to drain my system I'll replace my tubing anyway, so I cut it at the point it drains the majority of the loop and proceed from there.
I have actually drained my system to swap a CPU water block, replaced tubing while I was at it and had it back up and running in an hour, with no drain port.
I do a lot of testing and swapping out with my machine, so draining and rerouting is a regular routine for me.
If you're going to set it and forget it, you surely do not need a drain line, because when you do get around to changing out or cleaning, you'll probably use new tubing at the same time.
As a matter of fact I got tired of investing in pre-cut tubing lengths and bought a roll of it.
You'll get a better idea why checking out the 2 links below.
http://www.tomshardware.com/forum/275185-29-exploring-ambient-water-cooling
http://www.tomshardware.com/forum/282844-29-peltier-water-cooling#t2033960