To illustrate the success of the technique of prostate (rather gland-) milking I offer you a clip containing two scenes.
You see:
(1st scene) the guy having his cockhead stuck into a glas to catch his milk while working a dildo in his anus. Lightreflexions at the glas´ surface disturb the clear view of the oozing semen. So pay attention to the shadow of the glas and the first cum cast down on the sheets!
You get a better view in the second scene (beginning 26 secs into the clip): the cam is a bit closer to the glas in a similar position. You can clearly see the milk ooze into glas while the guy is massaging his glands (off frame).
The clip is fast forwarded by default to better show the harvesting of the juice. This means that collecting semen thru gland-milking (at least with this guy) takes much more time and effort compared to that and the volume achieved thru emission, let alone ejaculation.
For comparison please check out this clip of harvesting milk in this post covering the topic of emission!
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