Man, I remember when the 3D was the hot new boat. My friend sam had one, and nobody else did, and we were all jealous. It was like stern squirting was barely even worth it, because his crazy new boat made it so easy it was like cheating. Those were the days.
Anyway, flash forward to modern times. The stern squirt will be really hard in the 3D because it is sort of long, but you can do it. Don't cave in to the stupid suggestions about putting water or rocks in your boat. Learn to do it right. Your best bet is to find an instructional video from the 90s. They describe everything Phil said, and accompany it with pictures. One thing I would emphasize is to really rotate your torso (from your belly) so that you get a really powerful backsweep. You want to be able to look all the way back at your stern, and even have the option of planting your stroke over on the other side of your stern. The move will be easier on strong eddylines, but you haven't mastered it until you can do it on weak eddylines or even flatwater.