... does what it says on the tin... this is indeed that phenomenon. Pourquoi "chercher midi at tout haut cloque"?

More context needed is this doesn't seem right to you.

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Note added at 3 hrs (2022-03-12 16:44:03 GMT)
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Can you flush a washbasin? I think you can flush *some* washbasins.

With those you can't I think you can still talk of a "flushing sound" when emptying them.

The French and English terms appear counterintuitive to each other, the reason being that the meaning attributed to 'siphon' in each case is different.

In French, 'siphon' is a noun referring to the water trap (the U-bend) in a toilet, and 'de' refers to the undoing of that siphon.

In English, the 'siphon' part of the word is attributed to the verb 'to siphon', remove a liquid by means of the siphon effect.

Matters are further complicated by the fact that a toilet siphon, or at least the water-trap part of it, is in fact an inverted siphon. Compare this to when you siphon petrol out of a car's tank, i.e. it goes up before it goes down (if you don't know how to siphon petrol, learn quickly, you'll save millions).

Now, the back or downline part of the toilet is a 'normal' siphon, i.e. the water from the trap has to go up and then down into the drain.

So when the French talk about 'désiphonage' they are talking about removing water from the INVERTED siphon, while in English we are talking about the siphoning of water out of the trap and up, then down into the drain.

"siphonage - (1) The sucking-out of the water seal in a trap by the water falling down the stack or running down a drain. It can be self-siphonage or be caused by other fittings. With proper pipe sizes, layout, and ventilation, siphonage should not occur." [Penguin Dict of Bldg]

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Note added at 58 mins (2022-03-12 13:52:38 GMT)
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Note added at 7 hrs (2022-03-12 20:01:37 GMT)
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An answer has since been given that forces me to point out that siphonage occurs in two forms, induced siphonage as given elsewhere and self-siphonage.
Since all we have to go on is a gurgling sound, we do not know if it is the result of differential pressure or of something going down the gurgler, i.e. when it is flushed (which is another thing altogether, even if the head of water caused by activating the flush modifies the pressure across the seal and thus causes siphoning).

SELF-siphonage – atmospheric pressure causing water seal to be sucked out of trap
INDUCED siphonage – atmospheric pressure plus appliance causing water seal to be sucked out
https://blog.wavin.co.uk/a-remedy-for-falling-into-the-trap-...

As it is explained elsewhere, "Induced siphonage is when the trap seal of a fixture is siphoned by a different fixture on a common sewer branch line."

Siphonage
Siphonage can occur in TWO WAYS. It occurs when there is sufficient negative pressure (aspiration or negative pressure below atmospheric) to draw water out of the fixture trap. A negative pressure occurs in a drainage stack as water rapidly flows downward, drawing air into itself (entrainment). If the sheet of water flows past an unvented branch connecting to the stack, a negative pressure will also be produced in the branch affecting any trap seals in the branch. [this is INDUCED siphonage as explained above] If the negative pressure is great enough, then a siphon will occur. Also, a negative pressure occurs in the drain when a fixture is discharged. The discharging fixture may siphon an adjacent fixture trap that is not vented. For these reasons, venting is required to relieve any aspiration that may affect a trap seal.
Siphonage may also occur by a fixture siphoning itself at the end of its discharge. This is called SELF-siphonage. According to Recommended Minimum Requirements for Plumbing (BH13) published by the National Bureau of Standards (NBS), self-siphonage occurs when there is an unbalanced water column in an inverted U shape caused by the Ptrap as seen in the common siphon (see Figure 901.2b). Self-siphonage is also caused by the fluid velocity, or the momentum pull exerted by the moving column of water, whether the pipe is horizontal, vertical, or inclined. In a horizontal drain from the trap, the momentum pull in its full intensity is exerted at the end of the discharge (see Figure 901.2c). Therefore, such configurations are prohibited without the fixture traps properly vented to prevent self-siphonage.
https://forms.iapmo.org/email_marketing/codespotlight/2017/J...

Evacuation de la garde d'eau d'un siphon par évaporation ou par aspiration (en cas d'absence de ventilation secondaire par ex.).
https://www.google.com/url?sa=t&source=web&rct=j&url=https:/...
Comment eviter le Desiphonnage ?
Le clapet équilibreur de pression, ou aérateur à membrane, permet d'éviter la vidange des siphons d'une installation sanitaire. Il se pose par emboîtement à l'extérieur ou à l'intérieur du tuyau et s'installe obligatoirement en position verticale.
Le mot siphon vient du grec σίφων (sifon) signifiant tube.
Déchifonner/synonyme de tranvaser