Basically this is a bit of a myth, I think perpetuated by old cowboy films!
There's no way you could suck hard enough to remove the venom from out of your blood or lymphatic system. Most venoms are highly potent and only a very, very small amount is needed to cause damage. Most animals will produce a great deal more than is required to injure you so (for example a king cobra produces enough venom to kill 20 people in a single bite) removing enough simply isnt practical.
Not to mention (as in @imsodin's answer) the chances of injuring yourself in the process.
The only valid response to a snake bite is anti-venom and to get to it as fast as possible.