its used so the yeast that is in urine from drinking the beer will grow due to the heat from the piss and other sources. when it grows it grows into long rope like tendrils that stink excruciatingly bad and clog the pipes. the ice cools down the piss extending the life of the pipes and stalls the growing yeast.

i know this because i used to work in a very very busy club in vegas and a plumber had to fix a clogged urinal....it was very nasty