The grog pit was a flight of stairs which went down into the cellar of the school at the far side of the play ground. The sport was to find any unattended school bag and with a loud chant of "Grog Pit" the bag was cast down the stairs.
The poor unfortunate owner of the bag then had to descend the stairs while a mass of crazed baboon-like children press against the railing around the top of the stairs to shower them with as many big green balls of spit and snot as possible before they returned to the surface.
If the victim was particularly hated - as most of them were - they were pushed back down the stairs for a second (and sometimes third) shower of phlegm.
In extreme cases - namely, Tony - the usual rule of throwing an unattended bag was circumvented, and the bag was ripped from the victim's arms.