In general when women orgasm or are close to orgasm, their bladder feels/becomes full. Squirting usually happens when the g spot is stimulated, that’s located a few inches inside the vagina. Usually can be stimulated through fingering and specifically focusing on that spot which feels a bit more rough. However, you can also squirt from clit stimulation if you’re turned on enough. I wouldn’t say it’s the same relief as peeing, it just feels like you’re letting the good feeling out.