Praying at the porcelain altar
Vomiting down the toilet.
This is one of the colourful phrases coined by, or at least popularized by, the Australian comedian Barry Humphries during the 1970s in his Barry McKenzie column in Private Eye.
Humphries is a master at such earthy language and has a reportoire of phrase for vomitting, coined or collected in his native Australia. He could hardly do better than study the works of a previous master collector - Francis Grose. In the 1785 version of his A Classical Dictionary of the Vulgar Tongue, he lists 'Admiral of the Narrow Seas' as:
"One who drunkenly vomits into the lap of one who sits next to him."
See also: 'point Percy at the porcelain'.