No, even toilets in new buildings don’t flush well. I mentioned that I’ve seen toilets that pass a great deal of water—-more than is typical in the US and Canada—-and still can’t get rid of a bundle of toilet paper. Blockages downstream may or may not happen, but that’s irrelevant to my question because the toilets do flush, the water leaves immediately (implying that the drain pipe is clear and nothing is backed up from downstream), but the waste and paper don’t leave as quickly. The problem has to be something at or near the toilet. As I said, I suspect narrower drain pipes or deeper and longer P-traps.

That's interesting and you do wonder why these countries don't have better standards its not like work hasn't been done on this.

I used to work in hydrodynamics R&D (BHRA / BHR Group) and I shared an office with an engineer who had a project to analyse the UK's toilet designs and come up with design guidance for more efficient designs.

It was interesting to listen in on the call to the plumbing supplies company when he wanted to buy a couple of hundred toilets but instead of 200 of one type he wanted 2 of every model they had.

I did look at Computer vison / ML for this project, to measure flushing efficieny - but it was to expensive

> This occurs in a lot of the developing world. Older sewerage systems weren't designed to accommodate the stuff we flush down in the west.

Also, building code inspections may or may not be as strictly enforced in these countries, so even newly built things may not work properly.

It's not the just sewers though - because I've been to plenty of places that run on a private septic system serving a single building or a few buildings, and the rule is the same: no flushing the paper.

I have been told it's because of smaller diameter pipes.