I just stick my brewing spoon into the boiling wort and let it drip onto the refractometer. Why buy more stuff?
When I do that I get an elevated reading due to evaporation.
That's why corky regularly gets 110% efficiency 
If you scoop up a bunch and drip it on there I think evaporation will be minimal.
I thought it was the BLUE cooler mash tun.
Nah, the BLUE cooler mash tun is only good for a 10% to 15% efficiency improvement. I've found, through numerous brew day experiments, that any additional increase in efficiency is directly related to the quantity of home brew consumed.
+1 to the eye dropper, and I let it cool to room temp. Once I started doing that my readings became consistent and reliable.