A phrase first used by a young man called William from Central Queensland, Australia in an incident involving a dyslexic message on a get well soon card.
Originally spelt 'knok the troth'
Now in common usage as a colourful way of saying 'tap that' meaning attempt to have some semblance of sexual relations
Person 1: Look at her/him, s/he's hot!
Person 2: Would you knock the trough?
Person 1: Oh yeah!
When several people become severely drunk at a party and their is only one bathroom for those several people to vomit within. The sink and toilet are already occupied with the regurgitation of that nights partially digested morsels of former delight. The remainder of 3 or 4 people trying to find a place to vomit occupy the bathtub, huddling over the edge resembling farm animals flocking and jostling each other around a trough, which on a farm oddly enough resembles vomit.
Marc: Dude I have to open my anus's flood gates and release the passions of my bowls into the serene waters of the bathroom toilet.
Matt: You might want to prairie dog your turd and run to the McDonald's next door, there's a party trough going on in there.