My own (small number) observations (being in VERY close proximity allowed observation at the exact moment of release). In one partner, receiving oral stimulation to the clitoris while receiving manual stimulation to the G-spot (one finger moving in the “come here” motion) normally had strong vaginal muscle contraction and release. The net effect normally was a subtle sucking in sound followed by a “queffe” as Tom Lykis and Howard Stern call it. On this occasion, the queffe was accompanied by a thick (mucus like) fluid discharge (under force from the strong air release as her muscles quickly contracted the vagina). It came from her vagina, no question. The fluid was odorless, tasteless and clear.
On two other partners, they regularly discharged a clear thin fluid from their urethral opening during any orgasm. They both had discharges without odor or taste. In both cases, the first discharge would be quite voluminous while subsequent (if done soon after the first) were merely a few drops. Out of curiosity, I had one partner empty her bladder immediately before the start of orally pleasing her and only a few drops came out during her climaxes, until we had a few hours rest and started again. At that time her volume of fluid discharge for the first in her series of climaxes was large, the subsequent only a few drops of fluid.
I theorize that the fluid evacuated during their climax originates in the bladder (urine) picking up hormones and/or other glandular releases.
As for that first case, I will theorize it was vaginal lubrication being violently discharged by her extra strong contractions. I promise, the sound effects being a bit of a turn off was more than overcome by the quality of her contractions trigger my own climax. It was indeed as if I was being “milked” by her orgasm. Extremely pleasurable.