Knocking it out 

having a quicky, like f*cking in the bathroom

My roommate walked in as we were knocking it out in the kitchen.

Knocking it out by John Deere June 8, 2004

knockin' the bottom out of it 

Refers to particularly deep or rough sex. Implies that the man will literally knock vaginal walls down.

I'm sorry, Mandy can't come to the phone, I'm too busy knockin' the bottom out of it.

knockin' the bottom out of it by ray<3 October 18, 2008