"clit-pumping" is a term which refers to using a specially equipped vacuum pump for the purpose of inducing clitoral engorgement.
This engorgement is an erectile response, virtually identical as that of the male phallus. Clitoral erection involves the same kinds of structures, neural connections, and nitric oxide (NO)-mediated intercellular signaling, as does the male variety.
Although mechanical vacuum pumping is the usual way of achieving this sexual engorgement, there are others. Electrical and chemical methods can make the vacuum either unnecessary, or more effective, as may be desired.
A good beginning to the study of aphrodisiacs, is this article from the BBC, regarding a particular subset of the topic of sexual chemistry
Apomorphine enhances electrical stimulation, by mimicing or stimulating the release of dopamine in the brain.
Drugs such as sildenafil (Viagra) act by blocking an enzyme that indirectly prevents male and female erection, and is responsible for the male refractory period.
Finally, after a bit of science to help even those with severed spinal cords> to enjoy what God has given us:
the topic at hand.