Thank you for your nice replies!
And there are no bad effects from that?
I hope not... But I can't be sure how this works with other types of plastic, if that applies to the old elephants? (we don't have any white elephants, unfortunately). It's important not to leave it too much time exposed to strong sunlight, and the parts should be clean (not dusty, etc), or the solution can provoke some stains, I guess.
We had very good results with Steck walls from the castle (3666) too, and those parts are grey and not white. They look much better. Be careful, though, with the great Portuguese sunlight
The dolphin doesn't even need to be submerged?
It doesn't, that's the good news, there isn't much waste. The parts should be wet, and the sun must shine on it.