You and your girl are in the shower, and you don't really have much room to move around. So you both sit down facing each other. Her legs go over yours and you're sitting with your genitals next to each other. You take your dick and put it in her pussy. Then you proceed to move your dick with your hand in a jacking off motion in her pussy. Hence the Slip 'N Jack.
Mostly used in the shower, but also possible in a hot tub or a pool where you can't move much. Slip 'N Jack
by Scruffs June 20, 2009