I think the more common American expression is “praying to the porcelain god”.
…
My wife has another euphemism. She says “moment” for orgasm (as in, I just had a moment, so I need a minute). Except she uses it as a noun and a verb. You can moment, and you can get moment on the sheets.
The TV series “Bosom Buddies” had a scene where IIRC Henry referred to it as talking to “Ruuuuuuth” and “Raaaaaalph.”
My contribution to the thread: an “indiscretion.” This always struck me as odd, compared to “cheating,” “adultery,” and so on. I have a theory about this, but I’ll sit back awhile and see what others might opine.
Ah, the dreaded “moment” on the sheets, and the age old question who has to sleep on it.
I think the Brits have a lot of great euphemisms for death. “Casters up,” “popped clogs,” etc. as you just reminded me. I was thinking of this scene from Terry Gilliam’s Brazil, toward the end…
SAM Please, I've got to find Jill. HELPMANN Sam, I think I ought to tell you... I'm afraid she's upped stumps and retired to the pavilion. Sam looks blank. Thrown in the towel. SAM (takes a moment to work this out) Dead? Helpmann nods.
I once read that there is no actual quote-unquote “official” term for that fixture; a word that isn’t a euphemism (toilet, commode, WC), or a vulgarism (shitter, bog, throne).
We use ‘vaccuming the goldfish’ in our house, but not as a cover-up. It’s used to describe those times when you were busy doing all those little chores around the house that need doing, but are not ‘big’ enough of themselves to warrant “I’m going to do X right now”. Things like - general tidying up, getting the washing off the line, unstacking the dishwasher, emptying the kitchen bin etc. (Usually the things that no other person in the house bothers to do - you know what I mean).
“Why are you running late”? “Sorry - I was vacuuming the goldfish”.
To be specific, the definition was in YM, “The Right To Know”. In YPM, “The Grand Design”, Bernard asks Hacker “Isn’t conscription a courageous policy?”, and Hacker starts to panic.
I swear this is true: late 70s there was a big herpes outbreak. In reporting the outbreak, a modest newscaster coined the phrase (and I’ll never forget it) “inadvertent oral- genital contact”.
One for farting I’ve only recently seen “whispering a bum* secret”
*in the UK sense.
One I haven’t heard in the wild, but a supposedly upper-crust way of making sure guests don’t have to ask where the loo is*: "Let me show you the geography of the house’
*A euphemistic way of doing that is to ask “Where’s the… erm…?” with a suitably strained expression on your face.
The Doctor Who Red Nose Day short “The Curse of Fatal Death” introduced me to the phrase “bottom-burp”.
You British, you do love your buttocks-based humor…
You forgot my personal favorite “he’s pining for the Fjords”.
I got that one from The Young Ones (the TV series, not the Cliff Richard movie).
When you wake up to find your cat is sleeping on your face. 
All the flying posts here and no “uncontrolled descent into hostile terrain”?
Definitely. I posted a video of the very first Charmin Bear commercial here.
I’ve used “go water the porcelain”.
Well, there’s Controlled Flight Into Terrain (often abbreviated CFIT)
I hope this isn’t one from earlier in the thread.
Pubescent boys were being taught social graces, and were asked, “If you’re on a date at a restaurant, and you have to go to the rest room, what do you say?” One boy says, “Excuse me, I have to go pee.” Too coarse. Another says, “Excuse me, I have to go to the toilet.” Better, but not smooth enough. Third boy says, “Excuse me, I have to go shake hands with a dear friend, and I hope to introduce you to him later on.”
Excuse me, I have to shake hands with the unemployed.
AFA farts go, if it’s particularly noxious I’ll say I blasphemed in my pants. If there’s a suspicion of moisture content, I’ll say I was spray painting the inside of my briefs.
As I recall, George Carlin once offered “shaking hands with the unemployed” as a euphemism for masturbating.