I'm a new DivaCup user. I've been using it with my period while lurking on this community for tips on cup types and insertion techniques. After three days of frustration and practice, I finally think I found what works for me and I wanted to share:
I use the punchdown insertion method. I find that "punching" one side of the cup's rim into the middle of the cup allows for easier opening and sealing. I insert the cup with the "punched in side" facing down (simply b/c I'm better able to reach a finger on the backside of my vijay-jay than on the front side to check for leaks). Once inserted, I'm able to pinch the base of the cup 2-3 times. With my thumb and pointer finger I can feel the punched in rim moving upwards and out of the middle of the cup. I then use my finger to feel the side of the cup on the backside of my vijay-jay. If the side feels smooth, I know it's fully opened. Then I push the base up a little to seal it.
Unlike what the DivaCup directions mention, I haven't been able to rotate the cup to ensure a good seal. I also think the directions are a little misleading in that the picture shows a fully circular, open cup inside the vagina. Well that's nice, but my vijay-jay is not a hollow, round structure! Mine is more flat on the front and backside (or top and bottom, whichever you prefer) and rounded on the sides...kind of oval shaped. So I figure that even though the cup can hold 30 mL when fully open & circular, mine is always a little bit pushed together (oval-shaped) due to my shape. So mine can really hold about 15-20 mL before becoming full. (Fill up your cup with 30 mL of water, then squash it...yes, it overflows!) I keep this in mind in my changing schedule (on my two heavy days, I can flow 15 mL every 3 hours).
Also, be forewarned: if you have to take a #2, don't hold it, go to the bathroom. I tried to hold it and my cup started to leak. This makes sense anatomically since the rectum is right behind the vagina. I think my big bowel movement stretched my rectum, pushed on the vagina, and pushed on my DivaCup (I also don't think it was sealed right at the time, since this was trial day 1).
Good luck to all!