Allegedly played in the Rat Pit and Fives in the 'Shot. The turd was 'usually' placed between two beer mats to produce a more even spread, as plates usually broke and pissed off the bar staff... like it would - shit all over the place not withstanding.
It's doubtful if this 'game' actually ever existed, though stories of it are legion and are regaled with much awe. Think about it: would you put up with someone's shit all over your face (muckers or not)? The same can be said of Soggy Biscuit.