To take a shit down someone's anus after sodomising them.
From Bridget Jones' Diary.
Vodkas: 2 Cigarettes 10 (9 post-coital!)
Mark took me out for a fancy meal down Starburger. He then took me home and showed that his lovemaking tendencies leaned towards the Greek. Halfway through his stuffing my arse however, he insisted that I hold my gaping anus open whilst he took a shit down it. I said that this was impossible, he insisted that "all my previous bitches loved off roading."