Similar to a "tupperware" gathering, this type of growing underground movement is an ILLEGAL gathering where mostly transgender individuals inject silicone into their bodies to create curves, breasts, hips, etc. These parties are sometimes attended by non-transgender individuals also looking for a low-cost solution to the desire for cosmetic procedures. These procedures are performed by non-professionals in unsanitary conditions. This term was brought to light by the death of Vera Lawrence in March of 2001. The trial for her murder was coined the "pumping party trial".
The action of putting the needle into the skin of the paying customer and pumping the silicone into their body, followed by treating other customers afterward from that same gathering is the root of the term PUMPING PARTY.