c. 1500, "work with a pump, raise water or other liquid with a pump," from pump (n.1). The metaphoric extension "subject (a person) to a process resembling pumping" (to elicit information, money, etc.) is from 1630s. Transitive sense of "free from water or other fluid by means of a pump or pumps" is by 1640s. The meaning "to work with action like that of a pump-handle" is by 1803. To pump iron "lift weights for fitness" is by 1972.
Related: Pumped; pumping. Pumped up "raised artificially by a method likened to pumping" is by 1792; the sense of "excited, ready for action" is modern. Grose, in "Dictionary of the Vulgar Tongue" (1788) has "To pump ship; to make water, and sometimes to vomit."
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Harper, D. (n.d.). Etymology of pumper. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/pumper