Originally Posted by tophmck
I would have thought you'd get the best whirlpool by maximizing the amount of water going through the whirlpool arm, not it's speed.
It's sort of a momentum thing. Think about a really big tube. If you have 6gpm flowing from a 6" tube, you'll hardly have any velocity. The wort won't whirlpool faster than the velocity of the wort exiting the tube.
+1 on reducing the diameter only at the end...
I use a stainless hose barb. I think it's 1/4." If you go too small you could blow your silicone tubing.