I don't know if you have seen the show on Oxygen called Talk Sex, but here is a quote about the G Spot:
"During G Spot orgasm, a large amount of fluid may suddenly gush out through the urethra. It is difficult to estimate how much fluid is expelled. I have heard amounts ranging from one cup to 2 quarts. The G Spot fluid is colourless, (urine is yellow), it smells sweet like clover, (urine smells like urine), it does not stain the mattress, (urine certainly does)."
I highly recommend this show for fascinating sex questions & answers. Hope this helps.