unflushable

Etymology

From un- + flushable.

unflushable means that cannot be flushed. Lexicurio rates it Sui generis — a strength score of 87 out of 100.

adj

That cannot be flushed.“You may have heard an old crank in a big house ranting about appliances and unflushable toilets the other day.”
Not designed to be disposed of by flushing down the toilet.“The Sydney water team are hoping that by showing families the 'unflushable' and 'unsinkable' items, that the environment will be a lot better off.”
That remains in the toilet bowl despite flushing.

noun

An item that cannot be flushed.“Recently, I asked Moffat about the "unflushables" gag -- which leads to one of the funniest jokes in the British show -- and he said flatly, "That was not taken out by me."”