I keep venomous as well- you take the animal out of the enclosure using snake hooks. And no you cannot harvest and sell the venom- you would need hundreds of snakes to collect enough.
Oh. Maybe not to sell then, but can you harvest it it make the animal safe? ...I mean, do they ever run out of venom (so to speak) and have to stock up more before they can bite again? That's where I was going with the question.