One of the toilets keeps running some water all the time. The pot has been out of its place when the whole system was blocked, so I thought both events were connected. The fontanero explained to me one had absolutely nothing to do with the other.
The plumber was here to fix it today. He seems to be a real professional, un artesano, but unfortunately, his work only helped partly. It’s running less now. I am afraid the system is just too old or has been too long doing nothing.
Oh well, I learned again new words (artesano and flotador) and I now know how to fix a float in this system myself.