Articles similar to this amuse me. 
Quite an interesting visual.
“Don’t expect Queen Elizabeth to get off the throne: Here’s why”
When did “the throne” become the household toilet? Was it a saucy bit of satire against the world’s monarchies? Is it pure American slang? Any connection the the American Revolution and the freed colonies rejection of a new Monarchy?
I doubt it’s as fancy as that. It’s just referring to the worst seat in the house as if it was a big, fancy chair. Same principle as calling the big guy “Tiny”.
I thought it was British (probably music hall) humour. The ‘throne’ in those days would often have been in an outhouse in the back yard, and any seat further removed from a royal throne would be hard to imagine.
A connection to music hall humor was similar to the type of satire that I was thinking of. Benjamin Franklin was known for saucy humor that poked fun at the upper classes.
“Perhaps I’m too saucy or provoking?” ― Benjamin Franklin
The “when” is 1922, according to the Online Etymology Dictionary.
I don’t think it’s British slang, though. Probably American. Old references talk about the “porcelain throne” which would be funny juxtaposed against a king’s golden throne. An origin in the 20s indicates a time when porcelain bathroom fixtures were becoming standard so that would fit.
He kicked open the crazy door of the jakes. Better be careful not to get these trousers dirty for the funeral. He went in, bowing his head under the low lintel. Leaving the door ajar, amid the stench of mouldy limewash and stale cobwebs he undid his braces. Before sitting down he peered through a chink up at the nextdoor window. The king was in his counting house. Nobody.
Ulysses, Calypso. Pub. 1922, this chapter written much earlier.
Fun fact: Ezra Pound, the great enfant terrible, Joyce not to publish this section. (He had a similar prudish comment to Eliot for a portion of The Waste Land.)
ETA: Pound must have expressed his disapproval after he saw it in print.
Exapno, what’s your cite’s cite? Coincidence of date with Ulysses.
I vaguely remember porcelain throne from childhood. Eventually it got shortened to the throne.
I can remember dad grabbing the newspaper and saying he’d be on the throne awhile.
I took a quick look on the Google N-gram Viewer, which I’ve found to be a useful (although occasionally misleading and frustrating) reference tool. typically, it doesn’t give dates in the 1920s, as others have unearthed.
But, to my surprise, there are examples of “Porcelain Throne” dating back as far as 1848! Only these refer to an actual, royal king’s seat made out of porcelain. The references place these royal sieges in India and China. I wonder if people began referring to a “porcelain throne” not from their own coining of an ironical term by combining the porcelain of an existing toilet with the idea of “throne”, but by using recollections or occasional references to such actual Porcelain Thrones, seeing the ironic possibilities therein, and using the term directly for “toilet”. It would be much the same was the term “Sultan of Swat” , which was an actual* title of an Asian ruler, was applied to Babe Ruth – they took an actual title and applied to to Ruth – they didsn’t create the alliterative title “from scratch”.
*actually, the original references were to the “Akhwand to Swat”. I suspect it got changed to “Sultan of Swat” because most Americans don’t know what an “akhwand” is (I don’t), and for its alliterative value. And Babe Ruth probably would want to be called an “Akhwand”, anyway.
It’s certainly well-known in Britain today. On last week’s BBC News Quiz, they regularly read out accidental innuendos from newspapers and TV programs. One of the quotes this week was as follows:
It got a huge laugh from the audience, so assuming that the News Quiz audience is representative of the Great British Public, it’s a well-known euphemism over there. (Of course, this doesn’t necessarily say anything about where it originated.)
The Oxford English Dictionary’s earliest quote for this use of the term is from Ulysses:
1922 J. Joyce *Ulysses *ii. 38 In a Greek watercloset he breathed his last… With beaded mitre and with crozier, stalled upon his throne.
It is a very well known expression in Britain, though perhaps more likely to be heard from a comedian or someone speaking humourously than in everyday, non-bantering talk. As bob++ said, its probably from the music hall comedy tradition, and still used now by working class British comics who still carry traces of that influence. That could well be where Joyce picked it up from too (although he may have simply re-invented it for himself.)
I wold say it is certainly a much more British expression tan an American one. I don’t ever recall hearing it all the time I lived in America, although I will take people’s word if they say it is in use there.