The Milking Factory

 This is the earliest example (2011) I have found so far of the Milking Factory Idea, although I suspect more might be unearthed in due course. KW visualises an alien-like construct with youthful subjects secured to posts and even suspended in the air while their juices are coldly and continuously extracted. The subjects provide an interesting array of facial expressions ranging from resignation and bewilderment to orgasmic excitement at the moment of delivery.
I'd welcome information on KW's identity/web location

Kami Tora - Night Shift

Kami Tora's take considers the requirement for a little stimulation to ensure plentiful production. Thus the natural pumping qualities of the vacuum tube are augmented by electrical stimulation of the testicles. The choice of supplementary, giant dildo rammers is a little more questionable since such equipment, though exciting to watch, is not necessarily conducive to maintaining an excited erectile state except in the mind of well-practised recipient. However, one might expect to witness a spectacular ejaculation from time to time. The expressions of these captive milkers are more exaggerated suggesting that they are not experienced users, possibly even straight since their minder is a female nurse. Her calm indifference as she monitors their production efforts on a clipboard is a signal that the process may be unremitting for some time yet. Notice how the brackets holding the dildo ram to it's base resemble a human hand. Nice touch.

more Kami Tora (Note it's femdom!)

Destor777's version of the idea is much more humanitarian. The victims subjects are allowed to lie down on a platform (not obviously padded for comfort, be it said). They are loosely restrained, just enough to prevent interference in the process, and stimulation is limited to the pump itself and testicular electro-stim. Destor's recreation of the various stages of excitement and ejaculation is rather subtle and well observed and the loose restraint helps make that possible.

see Destor777 at Deviant Art

Kalabro - Milking Factory

Kalabro has acknowledged at his blog how he took his inspiration from Destor and he has effectively reworked the same image in his own style which will appeal to the lovers of bulkier, slightly older men. Personally I like his less spiky technique although Destor captures the movement of the captives rather well. Kalabro's innovation is to combine a catheter style draining bottle with a robotic pumping arm, perhaps the most aggressive approach to extraction of them all.

Kalabro also sketched other ideas for the scene. This one using the customary pumping sleeve and just a suggestion of anal stimulation. Kalabro always names his characters and that approach here suggests a group of buddies undergoing the same experience together.

Kalabro subjects Dave to an even tougher regime featuring testicular noosing and electro-stimulation plus a fearsome-looking dildo ram whose demanding effects are written across the subject's face and evident too in his straining arms and twitching feet. You can see the working of the drain tube/bottle device in this image.

The floppy-haired youth is a familiar face in Kalabro's stable of suffering and Jamie here seems to be destined to experience life after milking as his draining tube flies away at the very point of ejaculation and an unpleasant-looking robotic clamp-like device waits in the wings to take over. 

See more at Kalabro's blog

also my A-Z article on Kalabro