Every time the topic of squirting comes up, I'm honor-bound to post these two links..
Firtly, my wife's absolute favorite toy when it comes to pressing down on her Skene's gland/G-spot:
JT's Stockroom - NJoy Pure Wand
and this article on vaginal control:
Pompoir: The Art of Milking the Lingam | Tantra: Gateway to Ecstasy
That article has absolutely nothing to do with ejaculating, but my wife tried the exercises and was able to isolate certain muscle groups. The key to her was being able to isolate and relax in a certain way and letting go.
Being a devil's advocate here, let's say for the sake oif argument it is piss... So what? Her orgasms are many times harder when it happens and the release of endorphins is just so powerful, she just beams with contentment and happiness after it's done. <-- That, most of all is what's important.
Our main goal now is being able to accomplish that with my cock. Sadly the Njoy is the only thing that can make her squirt for now.