There is a gland called the Skene's gland(NSFW) (or periurethral gland) which secretes a fluid that is distinctly different to urine. I am surprised to see that the wiki article states that it is unproven that this gland is the source of the "font," because my college anatomy professor seemed pretty sure and stated it plainly as fact (she was an experienced professor and doctor of medicine). Though the origin is unproven as it were, you can confidently state that the fluid itself it is not identical to urine. It seems that urine may be present in some quantity during 'the event' though.