Point Percy at the porcelain
The 'porcelain' is the lavatory bowl - Percy is the penis. Lavatory bowls are actually made from earthenware but 'Point Percy at the earthenware' doesn't quite have the same ring.
This is one of the numerous slang phrases related to sex or drinking coined by the Australian comedian Barry Humphries during the 1970s and onwards. Humphries' Barry McKenzie column in Private Eye contained a fictional account of the doings of 'Bazza' McKenzie - the role model for the later creation Crocodile Dundee. In 1972, the character was used as the lead in the film The Adventures of Barry McKenzie, which contained a list of similar phrases:
Barry McKenzie (Barry Crocker):
Now listen mate, I need to splash the boots. You know, strain the potatoes. Water the horses. You know, go where the big knobs hang out. Shake hands with the wife's best friend? Drain the dragon? Siphon the python? Ring the rattlesnake? You know, unbutton the mutton? Like, point Percy at the porcelain?
See also: 'praying at the porcelain altar'.