Why Do Toilets in the US Often Require Multiple Flushes Compared to Germany?

[mugaliens]

I'm not really sure where to put this, but I found this to be an intriguing engineering question along of the lines of hydrodynamics. However, lacking any particular category devoted to that field...

Here's the issue: I spent the past four years in Germany. When I flushed my toilets, they flushed, completely, and without using tons of water - zero reamining residue. I settle in my apartment in the US, and when I flush, a large amount of residue remains.

But here's the curious thing: I flush again and it's all gone!

I'm thinking if each flush only removes 60% of the residue, by the second flush, only 16% will remain. But in reality, none remains.

Why is that?

 

[sophiecentaur]

This may be to do with the hardness of the water and a resulting film of limescale on the bowl. I have precisely the same problem in Brighton UK (Chalk water source and hard water) but noticed that, in Plymouth UK, where the water is very soft / acidic (straight off granite moorland), a single flush seemed to do the trick.
Does this effect happen all over Germany or just in one location?

OR, it could be something to do with your diet in the two locations?