If you're interested in depth
The second ring does not open so fast because it is an involuntary muscle unlike the outer ring. The outer ring is also partially involuntary, but you can learn to relax it indirectly by deep breathing, or pushing your hole out. If you want to enjoy depth, you can do the same thing with the second ring, the constriction between the rectum and sigmoid colon. But it is more difficult.
The top should thoroughly lube the ring first. Inserting one or two fingertips through it, he then exerts only moderate pressure with his whole hand in a swan-shaped position. He then holds his hand in place while the bottom pushes the ring down over his hand. When the bottom releases the outward push, if the top maintains only the same amount of pressure, he will be drawn in deeper. Repeat as many times as enjoyable.
The push can be accomplished as you would for a bowel movement or even just tensing up your abdominal muscles and then relaxing them. For practice, try this same thing with sizable didoes, but donít just force the dildo through the ring--that's where most of the reported injuries occur, either in solo play or with a partner.
You will also sense much less discomfort, if you are participating by pushing out, than if you just lay there and let the top make all the movements. When this technique works the top usually gets so turned on as his arm sinks in, that he's not going to object.