you might want rates on for this one, but here's how I do it with 30degrees on everything.

From full power level flight pull up to 45 degrees, roll right to knife-edge, wait a second or two, then apply full left aileron, full right rudder and full down elevator, and hold.

The plane should yaw until its vertical while spinng about the CofG, kinda like a waterfall, but all the time sliding to the right.
Try to see how long you can keep it in the tumble, and how many gasps you get from the gallery.