Stick his cock into her ass?

The Doctor moved as close to the edge of the tub as he could, and guided his cock up to Clara's sweet bottom. He pressed his swollen cock head against her puckered asshole.

"Oh god, yes," Clara gasped, her voice raspy with anticipation. "That's what I want."

The Doctor slowly pushed his cock past the resistance and into her ass. He slowly pressed himself in his entire length as Clara's legs wobbled slightly with excitement-induced weakness. Then he pulled it out slowly. He pressed it in again. And out. Slowly building speed as his cock started to get slick with the sudsy water and her asshole started to open more and more to his throbbing manhood.

He grabbed her hips and began to fuck her ass a little harder; still not as hard as he could, but hard enough, feeling his body slap, slap, slap against her sweet buttocks. Clara yelped and moaned as he fucked her ass from behind.

"Good god!" she groaned. "This... is... so... fucking... amazing!"

Her tight asshole gripped his cock tightly as if it wanted to drain him of every last drop of semen. After only a few minutes of this he was ready to oblige.