Under the pump - for being very busy, feeling the pressure (like that caused when using a pump to inflate), almost at bursting point.
How are ya, mate?

'Far out mate, been under the pump!'
by BVB1 February 15, 2019
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When you masturbate then do a backflip as you climax so that you ejaculate on your own face in mid-air.
Person 1: "Is that a bit of ranch dressing on your face?"
Person 2: "Nah, I've just been under the pump"
by Lord Of All Things Sasquatch November 10, 2020
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