Another common name for a toilet like this is a "Thunderbox". Some country houses in England were still using them into the fifties and sixties. A few had quite sophisticated one off flushing mechanisms with brass fittings.
How odd. My grandmother would call it a "throne". I never heard anyone else call it that until now. (She would only say that when referring to my grandfather, "he's on the throne" perhaps she had some resentment over him as "King" of the house and showed it in that way.) a rude story maybe, but your title brings back the memory O_o
She was German so I wondered if her mother brought the expression with her on the boat XD I thought it was my Grandmother's own humor until this title. BTW (and I should not obsess on criticizing DDs but...they beg for it too often) omg there is a "throne" image as a DD today. Titled - Sleepwalk In Rome. hahahaha What the hell is that? Does Calvin Klein want people to laugh ? if so, it is a success!