Double piston 

When a man or woman puts both of there fists inside a butthole or vagina and moves in conjunction While one fist moves down the other goes up. Like a engine piston.

I was screwing my wife last night and decided to give her the double piston elbows deep.

Double piston by Irishrover18 January 12, 2017

Double Piston Chesty 

Application of aerosol deodorant with a blast under each armpit followed by a slash across the chest.

Come on, dude, we're going to be late to meet the chicas. Finish getting dressed and let's go!

Okay, just a quick double piston chesty and I'm ready.

Double Piston Chesty by rickbrunernyc August 3, 2009