Athens Hotel Question

Hmmm, we were explicitly asked Not to do this for all the hotels and public facilities on our RS tour but we didn’t stay in new ultra modern hotels where it might be different.

I don't think that's a thing in Athens, or any of the cities. It's the more rural areas. I think we ran into that in Monemvasia, on the coast of the Peloponnese.

That’s the case everywhere I have been to in rural Greece. Modern hotels in Athens less so.

We stayed recently in anf very much liked Inn Athens and The Modernist.

Throwing paper in the toilet is pretty much a no-no all over Greece: cities, islands and rural areas alike. It’s just what is. Even when you find a hotel that lets you flush paper down the toilet, then still 99,9% of museums, tavernas and bars in every neighborhood in Athens will urge you to throw all paper in the always present bin, for same plumbing reasons.

Just about everywhere I've stayed in Greece including Athens says not to throw toilet paper in the toilet but in a small basket next to the toilet.

There's usually a notice next to the toilet asking patrons to do that.

There's really nothing unsanitary about it and it helps keep the sewage system working properly.

When in Greece do as the Greeks do.

Take a look at InnAthens. Our stay there was very enjoyable, and may be what you are seeking.

I've stayed at the Athens Capitol Hotel--MGallery Collection.

Very nice modern hotel. One block from Syntagma Square.

You have a choice of flushing the toilet paper or not.

Please do use the lidded bin and do not throw anything down the toilet.

If there is a bin use it.

Please do use the lidded bin and do not throw anything down the toilet.

If there is a bin use it.

Many modern hotels in Athens treat their waste so that it is not a problem for the ancient sewer systems in Athens. You will usually see a sign in the bathroom letting you know it is okay to flush your paper.

“Many modern hotels in Athens treat their waste so that it is not a problem for the ancient sewer systems”
Not many at all, maybe a few, apart from that as already mentioned toilet bins will be encountered anywhere outside the hotel too. I visited Greece about 30 times on holiday, lived here almost 20 years & spend all my holidays travelling around Greece, I have never stayed anywhere yet that you could flush! Safest to assume that it’s likely you’ll need to use the bin & be prepared for it than to hope for somewhere that you can flush. The comment ‘if there’s a bin use it’ is the best way to decide what to do.

Athens Capitol Hotel was one that advised it permitted flushing toilet paper down the toilet. I would like to confirm with someone who was there whether this is true.

Just out of curiosity, I looked at photos and videos of the rooms at the Athens Capitol Hotel. Although you don't see the usual little sign saying "Do not throw toilet paper... etc ", you can still see a small bin right next to the toilet.

This means that even if it's not mandatory, you can adopt Greek customs and put the toilet paper in the bin.

https://maps.app.goo.gl/t6fePh1RNyjwm4Ve9

https://maps.app.goo.gl/bMSam8zLZGLDLKpD7

Really if you intend to visit Greece you may need to come to terms with the toilet paper issue, unless you intend to stay in your hotel for the whole time.
Please do not see this as a criticism but it is a reality for everywhere in Greece and you do not want it to impact your vacation.

Based on OPs posting history it looks like Athens is only one of many locations in Greece on the itinerary.

As expat-nomad says, you need to make peace with the 'special can' in Greek bathrooms, because it is the situation everywhere.
They all had lids and the hotel staff tends to them daily. ( at least the hotels that were on our RS Greece tour, which I suspect is the common practice)

I've stayed at the Athens Capitol Hotel (MGallery.) We were told we could flush toilet paper, but only toilet paper, in the toilet.

There was a bin next to the toilet for those who didn't want to flush.

There are always bins next to toilets in Greece. That's not an indication that you should not flush your toilet paper. If a hotel really has issues with flushing toilet paper they will normally have a clearly visible sign not to do so.