I've also had a bit of a girls look and could find any either, but by no means did I have an exhaustive look.
Seeing as though I'm dumping the coolant anyway, I was thinking of just running a 1/4 NPT I think they are tap through it, no drilling required. Others have done it in situ, grease up the end of the tap to catch the swarf and as the coolant runs out it washes any escaping deris out with it.
Edit: 1/4 NPT.