Hm. The Russian sentence means the person is in that room with an object that provides joy and relief to those in need. If you mean reflecting on times past while sitting on top of a man's porcelain best friend, this is not what the original sentence says.
The precision of the sentence in the title stops at the door. We do not know what "he" is doing inside that room. :) Whatever you call it in your variety of English.
The toilet bowl is «унита́з», though, using that would not be the most discreet way to describe someone using conveniences. Use "сидеть на унитазе" if you really need to.
A more roundabout way to say the same is «сидеть в туалете». If someone сидит в туалете (is sitting in the bathroom) it pretty much means they are sitting on a toilet, unless there are chairs, beds and couches in your bathroom, too. Not the best option, too, but less harmful to people ears than «сидит на унитазе» (I mean, not everyone wants to imagine THAT in detail).
I think the phrase "he is on the toilet" doesn't imply literally sitting and can be used for a man or woman regardless of what they are doing and in what posion they are doing what they're doing. It's like saying "he is on the phone" or "she is on the computer", which doesn't require sitting on top of any of these devices.
Thank you for your responses Shady_arc! I also put "on the toilet" (American here, btw), and I think it should be accepted. When we say on the toilet, we don't know if he is actually sitting and taking a dump. Perhaps it's a bit vulgar way of saying it, but I use it whenever someone's using the toilet (also, I now wonder if "using the toilet" is accepted?). If we know he is actually sitting on the toilet, we (I) would say something a bit more descriptive if we (I) wanted people to know exactly what he was doing:)
Pro Tip: try to understand the cases per se instead of struggling past them... when I started learning German, I wasted way too much time with randomly finding patterns in cases when it is actually much easier to learn what the cases themselves are! Now (after I solved that problem inconveniently late) I have a fairly good idea of what accusative, dative, genitive and so on mean, i.e. when they are used, so it's all down to practice now, just like vocabulary, without going the extra mile and grinding your brain to exhaustion with the actual implications of the case. Tl,dr; learn what the cases are by themselves because most languages have cases and once you grasp it, there is nothing to stop you.
As an american who just encountered my first russian " bath room" with no toilet I can say its very confusing. So if a russian person is taking a bath they first go to one part of their house to relieve themelves, then they pull their pants back on and walk to another part of their house to take their pants back off to take a bath? It seems impractical.
They are usually right next to each other. Having a bath and a toilet in the same room actually makes little sense except for plumbing. That said, joint bathrooms do exist in Russia—either if you go for smaller, cheaper apartments OR if you are aiming at a home with multiple toilets.
The practicality of having a bath-toilet-room is marred by how awkward bathing is when a family lives in such an apartment.
So, believe it or not, joint bathrooms were at some point a downgrade. They take a little less space than two rooms and technically give your family the same functionality.
You are supposed to hear a short "f" sound between он and туалете.
Try reading the sentence yourself. Only pay attention to the pronunciation. :) Unlike in English, т and н are pronounced close to your teeth. В is rather relaxed, with your lower lip merely touching your upper teeth.
When used to express a location, в and на require this form. Depending on the type of noun, it ends in -е or -и (e.g., в воде, на земле, в молоке, на стуле, на телевизоре, в интернете, в дне, на лошади, в химии, в здании).
(but a number of short consonant-ending masculine nouns use the stressed -у ending instead, e.g., в лесу, в году, на полу, на углу, в аэропорту, в раю).
The spelling "toilette" is rare in English (I haven't seen it before); it refers to "toilet" in the sense of "the act of dressing and preparing oneself" or "the dress or costume of a person".
It does not refer to a room.
And "toilet" (which can have other meanings as well) usually does not refer to a room, either, but most commonly to the fixture (often made of porcelain) that one sits on, which is not what Russian туалет means.
American English is no more objectively "wrong" than any other dialect. Duo, being based in the US, uses American English as its standard. "He is in the toilet" is accepted for the sake of Australian and British speakers, despite the fact that this creates immense confusion for Americans.